I used Air Video quite a bit this weekend and it seems to work fairly well - occasionally I would get a lack of response. However I don't know if that was a problem on the client or server side.
I have only used Air Video for streaming but I believe it can also convert and store on your iPad.
Air Video makes a great companion to PVR software. I use SageTV to record TV shows and then Air Video allows the iPad to be a great portable playback device, although a native Sage app would be better since it would also allow you to stream liveTV.