2 issues for me and both are show stoppers as far as I am concerned.
1 - Series Record no longer works for weekly shows.
2 - Windows Movie Maker and pretty much every other piece of editing software does not recognise the new .wtv file format so you can no longer edit out the leading and trailing garbage from any recording or edit out the ad breaks (in fact trying to open a .wtv file in movie maker will cause it to crash).
I also found the picture quality worse with the tv pack and suspect the new decoders are not up to scratch (my opinion only so dont flame me if you disagree).
Couple of other things I noticed..
..The channel scan now seems to work in reverse - i.e. BBC channels are detected last now whereas before they were detected first.
..What appears to be yet another new bug - occassionally changing channels will just result in the audio playing but the video looping the last few frames from the previous channel (I have to close and reopen media center to get it going again).
..Recording radio stations now takes up a ton of disk space because for some stupid reason it still seems to record the video stream (even though there isn't one).
If you are tempted to install the TV Pack please make sure you have a fresh restore point or better yet a complete backup so you can roll back the changes if you are not happy with the outcome.