I used a Samsung LN 630 120 hz 40-inch LCD TV with both an old G4 Mini and with my 2010 MBP as a test. It was fun to watch AVIs, WMVs, etc and to do iPhoto from a distance. I have a wireless Magic Mouse and a Wireless Apple Keyboard.
However, the 40 was way too big for using as a desktop monitor. It might be OK if it was "further back" on the desk, sitting in the background or on the side to use a "workspace" to extend the desktop or to watch video or monitor newsfeeds. I also had black bars running vertically on the left and right side, which did not surprise me or both me. Some peole who want to fill the whole screen would need to research further to see if their particular Mac is totally compatible with the particular monitor they are thinking of buying.
I would look at around a 32-inch TV, and you can save money if you are willing to do 720p. If you want to do 1080p though and/or 120hz, you are looking at TVs that are as expensive or more expensive than cheaper monitors.