I'd say as a general rule, not really. TVs that can do up to 1080i will probably have a max PC resolution of about 1368x768, and 1080P TVs will have a max resolution of 1920x1080. 1920x1200 is fine for a 24" monitor for example, but considering you're only likely to find 1080p HDTVs which are at least 32" big it's not that great.
Also there are two more caveats. For a start, HDTVs are designed to be viewed from a distance. If you view one from up close as if it were a monitor, the pixel density's so low the image just won't look right. Think of it like standing right in front of one of those big LED screens you get in city centers or concerts. Secondly the 16:9 aspect ratio was not designed for computers. This is despite the fact that monitor manufacturers have recently made more 16:9 than 16:10 monitors to cut costs, bleh.
Besides all that, if you just want a second monitor to plug a laptop in for a presentation for example, they're great, but so far as using one on a day to day basis is concerned, don't bother. Either buy a TV, or a monitor, or both, but don't buy a TV that's supposedly also a monitor, because chances are it's not a very good one.
EDIT: A a small note, buying a monitor that also has a HDMI input is a different matter. Of course they won't have a freeview tuner built in, and you'll need to plug the freeview/sky/freesat tuner into separate speakers, but if you do it this way round you'll get a good monitor and an above average TV, assuming you make sure the viewing angles are good.