I'm betting my technical knowledge here is way below that of many others posting... but it seems plainly simple (to me). IF no problem before Lion install and IF problem after, it's a Lion problem. I'm confused (but not looking for explanations, thanks ; ) on why everyone is talking about their routers and firmware.
Slyclops, thanks for the clarification of DNS and relevance. Good to know. I'll only add that when I first started getting the dropouts, I would often have four full bars and even an indication that I was connected in the Diagnostics Assistant part of the Network preferences (all green lights)... but still couldn't connect (i.e. spinning wheels in Safari, no Mail connection to server, etc). And that only started with the Lion install too, but went away with the addition of "8.8.8.8" to the DNS settings. Not sure why, but there you go. I present it as possible useful info to whoever might be working on the fix from Apple.
Just an extra note... there are a lot of people steamed up over this, and justifiably so. You pay for something, especially something from the company that advertises "it just works," and you don't expect this kind of hassle.
But it made me chuckle to remember how it was when Jaguar first came out or whatever big cat the first edition of OS X was named after. Wow, was that bug-ridden. It was leagues cooler than OS 9, which I left behind with great reluctance.
Remember rebooting to run OS 9 programs? The outcry then was huge from those who felt OS 9 was still superior. And I couldn't tell you how many times I had to re-install and/or run Disk Warrior on both the computers in our house because the directories needed rebuilding in that early iteration of OS X.
Yet these days, I'm more of a Mac zealot than ever.
Go figure.