Even though Adobe has said that all Froyo enabled phones will be able to play Flash, today they are saying that this is no longer the case, and some phones with Froyo won't be able to support Flash. Why the change of mind?
Froyo is the pinnacle of performance for Android, and I suspect it's as fast as it's ever going to get, because from now on Google will focus on other things like UI, battery management and other features. Of course, as they add these things they will try to keep Android as performant as possible, but it's not going to have the same raw performance as Froyo.
Since manufactures are going to prefer the Froyo version for their lower end handsets, this spells trouble for Flash. Adobe is announcing that Flash will play only on handsets with a 550 Mhz CPU with hardware vector FPU support for phones with VGA resolution, and 800 Mhz Cortex A8 CPU with hardware vector FPU support for phones with WVGA resolution. As these resolutions rise, even stronger CPU will be needed to support Flash.
If you want the best Flash experience and you're looking for a new phone, I suggest you wait for a dual core CPU phone with hardware acceleration for Flash. That should offer plenty of performance for Flash sites, whether they are optimized for it or not.