I will use a word like hatred when the original post contains a stereotypical Microsoft basing response to a product that they have likely never used. That is what was being emoted in the post.
In terms of PVRs I have extensive experience with TiVo (Series 1), XP MCE, Vista MC, Beyond TV, SA8300HD and limited exposure to Sage and the Bell PVR.
The products offered by the cable and satellite companies in Canada are very weak. The Rogers PVR is very slow, has only rudimentary search capabilities, has a UI that is ugly, doesn't allow extension to other TVs and does not allow you to move content to PCs or DVDs. One positive is that it simplifies connection to your HT and it is easy to add hard drive space, although there is only room for one additional drive. My impression in limited exposure to the Bell PVR is that it is slightly better but not hugely so. You cannot do placeshifting with this device unless you buy a slingbox. You cannot use this device to watch internet TV types of shows other than the VOD offered by your cable co. The Rogers VOD is very buggy and often crashes.
XP MCE has a very nice UI with full search capabilities and also works as a front end for all of your media content such as photos and pictures. There are very good add-ins for features such as managing your DVD collection and place-shifting. You can also use this product for watching pretty much any file type that you can find. Content can be converted to other formats and burned to DVD. You can buy Media Center Extenders that allow you to play content from your HTPC anywhere else in your house. It also comes free with the OS, assuming that you buy it as an OS. It is trivial to add more hard drives to your system as you could have several terabytes of hard drive space if you desire. You can use tuners connected to analog cable, digital cable boxes and satellite boxes. Channel changing is somewhat slower as you have to use an IR blaster. In terms of HD there is no way to get HD into MCE other than OTA. PVR software from MS respects CGMS-A flag which is problematic for Canadians - it appears that only MS respects this flag. MCE extenders work very well with some limitations - they do not allow you to view digital TV and they don't work so well with video formats other than MPEG-2 and dvr-ms.
Vista MC (WMC) comes with Vista Home Premium and Vista Ultimate so it is likely the most installed PVR software on the planet but I bet only a small minority of people running these OSes actually use the product. It is the only PC based PVR software that allows you to record cable HD channels but that requires a whole new PC with CableCard tuners -you cannot add these tuners to an existing TV. The UI in VMC is a fair bit different from MCE some folks prefer it, I don't. The library management features of VMC are not very intuitive and VMC seems to believe that all card readers on your PC are good places to store video files. There are now V2 extenders available that allow you to extend VMC throughout your house. One model is to build a system with multiple TV tuners and throw it in your basement. You would then put extenders at every TV to act as the front end to all of your content.
You can use an XBOX or XBOX360 as an extender to Vista MC or XP MCE. The UI is pretty much the same as what you would have at the PC itself.
The TiVo has an excellent UI and TiVo has done a good job of making it easier to get content off of the device although there can still be some copy protection at times. The only TiVos sold in Canada do not do HD - there is an HD model available but that can do OTA and CableCard which isn't available in Canada. TiVo probably provides most of the other features of MCE except that I do not believe that you cannot play various different types of video files such as DivX. TiVo has very good search capabilities, it allows you to record series, etc and it is very good at organizing content after you have saved it. You can add hard drive but not as easily as with HTPCs. I believe that you can also share content across TiVos in your house if you have several TiVos. One downside of the TiVo is the cost of $12.95/month - none of the PC PVRs have a regular fee.
BeyondTV is more focused just on TV - it does not have the music, photo, etc. stuff built into it but there is a sister product called BeyondMedia. BeyondTV can do most of what MCE does and it has a feature that can automtically remove commercials and re-encode your files into more efficient formats such as WMV or Divx. I do not believe there are any extenders available for BeyondTV. BeyondTV is a commercial product - you have to pay about $70 for it. Just like all of the PC based products you can use BTV with HD OTA and with non-HD cable and satellite, typically with and IR blaster. You can placeshift with BTV.
If I were to start from scratch I woule likely go with SageTV. It has pretty much all of the features of MCE and it appears that you can customize the UI as there is an MCE-like interface called Sage MC. Sage sells extenders that can do HD and these are cheaper than MS's V2 extenders. Sage seems very proactive at improving there product, much more so than MS. Sage has said that they plan to support the Hauppauge HD PVR product on release or shortly thereafter. They also take more of an effort to get their product to work with more different types of hardware. There is a placeshifting option for Sage. You can also get Sage to work on a Windows Home Server box which is something that you can't do with MS's PVR software.
MCE and VMC store video files in the dvr-ms format. That is essentially a MPEG-2 file with metadata included. It is easy to convert this file type to MPEG-2 as it does not involve re-encoding. BTV (and I think Sage as well) store files directly as MPEG-2 and they have other files, such as XML files, to contain metadata such as program name, channel, etc.
Note that all of the PC based PVRs (MCE, VMC, BTV, SageTV) are full PCs which is both a good and bad thing. The good thing is that you can use them for other purposes such as web browsing or you can throw in a BluRay drive for just over $150 and have a BluRay player. It is also pretty easy to add codecs if new video files become popular. Assuming that broadcasting of TV shows over the web takes off you have a way to view such content on your HT. The bad thing is that it may take a while to get them properly configured and they are more prone to crashing than a TiVo and perhaps a cable box although Rogers cable boxes have a tendency to crash when access VOD. All of the PC based solutions and TiVo have excellent search capabilities and allow you to easily record an entire series - that is not the case with the Rogers box.
Is that precise enough?