I've just had a look at the site stats for this month and it shows that 8.7% of users are on 800x600 (down form about 14% over the last 12 months), so they'd need to use horizontal scroll a bit. Just over 50% have 1024x768 and everyone else has larger than.
If you're looking for a larger screen, I've just bought a new iiyama Prolite E1900S and it's awesome. It didn't top the recent group test of 19" monitors in PCPro magazine because it didn't have a swivel base etc
, but for image quality it's outstanding and that's all the matters to me
Stu