I actually experimented with not using flash to see how much I actually use it. The only area I notice a difference is watching embedded videos, which are almost always encoded for flash. So if I go to most news sites and they have a video I want to watch, it won't work without flash. That's the main problem with not having flash on the ipad, you'd be crippled in watching video.
Also, internet games almost always use flash. Yet, I think most popular internet games will be ported to iphone specific apps. Already mafia wars and livepoker have iphone apps. I don't see why Zynga wouldn't port farmville to an iphone app, since its currently very popular. I would suspect most other game creators to do the same, especially if the ipad becomes as successful as the iphone has been.
So, personally I can do without flash, but am crippled a bit in terms of video mainly. I hope sites start moving towards non-flash video, but until then its a definite problem having no flash. You are getting a different internet experience than anyone else who is using a real computer. Yet, it still won't stop me from buying an ipad!