I'm relatively new to the whole Boxee thing so having fun playing around getting it to work exactly how I like. One of the disappointments for me was the lack of an app for TVCatchup. This is, for me, the closest you'll get (for now) to an ideal solution for playing TVCatchup...
1. Go to http://www.tvcatchup.com/ and login / register
2. Visit the channel list and select the channel you watch on an regular bases e.g. BBC One
3. Click the "Watch [channel] in our 'old' web player" link below the player (I can't get the new player to work)
4. When the old player loads simply click the Favourite button in the top right
5. Repeat steps 2 - 4 for all your favourite channels
I also favourite the channel list (http://www.tvcatchup.com/channels.html) and the TV Guide (http://www.tvcatchup.com/guide.html) although links from these open in the new player.
Now, to play live TV just go to Web in the menu and select your channel from your Favourites list.
Anyone else got a better solution (for the UK), or tips to make the experience even better?