Depends on the PDA.
If you get a "standard" one with a 240x320 pixel screen, it's not all that enjoyable. Very few screens scale well to that small a resolution. It's strictly an "emergency browsing only" thing... (whatever emergency browsing is
)
If you get a PDA that has the possibility to run the Opera web browser, you might be happier; they have a really good small screen rendering mode that liberally alters how the page is displayed to make it readable on a small screen. There is no Pocket PC- or Palm-version of it though.
If you get a PDA with a full VGA screen like a Toshiba E80x you'll be better off however. You'll have to tinker a bit with third-party software addons and patches to make it work in VGA mode with most applications but once you do I'm sure it is quite usable. Of course, you need good eyesight to view 640x480 on a screen four inches large.
Palm and Sony have machines with 320x480 resolutions too and while I haven't used one myself, they should probably work passably at that resolution.
In general, though, I find surfing on a small screen to be something you do strictly as a last resort if you can't get at a machine with a real screen.
