If you buy a "nettop" style HTPC (Atom, ION, etc) then it'll be obsolete much sooner than if you get a HTPC that has a fast general purpose processor.
Well, like I've said a few times before I think getting a Intel Sandy Bridge-based processor is the best choice for anything but the lowest-end HTPCs. If you want a fairly compact system, then you're looking at min-ITX motherboards like this Zotac board. Notice how Sandy Bridge uses half the power of the AMD 890GX (both load and idle power) while still winning the benchmark wars. This is great should you choose a small HTPC case since, not only is there less heat generated by the system, but you can get away with a less powerful (and smaller) power supply.DanceswithLysol - Could you please name a few HTPC brand's that would fit your description of a fast general purpose processor?
The issue with Linux/MythTV is that there are still plenty of holes in driver support. The last time I looked into it I couldn't get the Hauppauge IR blaster working, for example. These problems are difficult to mitigate short of buying new hardware or writing your own driver.Having said all that, Linux/MythTV is the OS of choice for HTPC, but if it is too exotic for you then look for a Windows-based HTPC app or solution that properly supports Canadian OTA and that respects your consumer rights.