I had a tiny computer years ago and it was a good machine, my brother has it now and we have had no trouble with it. I really like building my own comps but there is no way I could build one with the spec for that price so I am tempted to go for it.
Seems like a very good deal,only thing that may let it dow (but not at the moment) is the 128meg graphics, On top at the moment but who knows in a year or so, 256mb would have been the icing on the cake, but still a good system. (not sure if WIN XP Home version will have support for 64bit system, might be an idea to check before paying for something that may not run at full speed).
may sound negative, but you did ask for our opinions, if i had £800 to spend, i would probably buy it myself, but see if there is a possibility to upgrade to 256 MB graphics.