I've had it since I updated my Desire to 2.2, and it works pretty well despite what Steve Jobs said about not having it on the iPhone and iPad. Sure, demanding Flash videos/sites slow the phone down, but they'd slow a slow computer down that was attempting to play it as well. If I visit a website on my phone with demanding Flash content on it then I get an message saying the website is not optimised for mobile. Yet there are websites with Flash videos that play very smoothly, such as the Zero Punctuation videos.
It can be slow on phones in some places now, yea, but when more powerful smartphones are released then it can only get better.
Flash Player 10.1 can be downloaded from the Market by simply searching for "flash". It takes up around 12MB of space once installed and can't be moved to SD card, so make sure you have sufficient space on your phone storage. (I like to keep above 25MB of storage free on my phone, as any system updates require 25MB of storage to perform the update).
To find out if your Android phone "works well" with Flash, then just visit this website.