Web browsing my pre-android unit is solid, from the other guys I've chatted with that have the android, they say it's pretty awsome. Nothing IMO is going to replace a full blown laptop, but for quick tasks I don't have any issues with the Opera browser on mine (android version obviously does not use opera).
The real power of these units is unlocked with the additional purchase of a battery dock. It's a dongle-like thing that has a backup power supply, gets you about 1.5X the battery life. Also opens up the unit to act as a usb host (has standard usb plug on it), this allows you hook up additional hardware like usb keyboards and mice. When I need to take some notes in a pinch i pull out my collapsable keyboard and type. I'm also pretty into my photogrophy, plug the camera into the battery dock and dl all my pictures for storage and viewing on that hi-def 5inch screen, no need for a computer to take pics off the camera in the field.
Now, the main downfalls are the price and the support if something goes wrong. If you have a decent Best Buy near you that you can just replace the unit hassle free directly through best buy, great, if not, Archos will repair your unit, it's just pulling teeth to get a hold of anybody. Another potential problem is the bulkiness of the HD based higher capacity units. I'm a big guy so I don't have any issues, but if your a smaller guy or a chick, putting this thing in your pocket could be a problem.
I have had my unit for a year or so now and no problems (except that I REALLLY want the android verison now playing with my droid and seeing the OS in action). I use mine primarily as a media player, with 250gigs of storage, the ability to load free flash games off the web, that wonderful screen, and the file support that it has, I don't have problems recommending it to a fellow geek. If you don't like tinkering with your gizmos and just want something to work, this might not be your thing, but chances are if your in android forums that you like to tinker and customize anyway...