I'm not expecting my DX to be a completely different phone once froyo hits, all I really want is...
1) The ability to have flash. Now that being said I realize it will be a bit buggy for now, but hell let's get real for a moment already, this is the very first mobile OS able to even run it... So I'm not exactly expecting perfection right out of the gate. But I will expect it's performance to improve with future updates. But heck it's better than not being able to open flash sites at all, which is what I have now with 2.1.
2) Some improvement in battery life. No I'm not expecting it to double or tripple my battery life, but even a subtle improvement will be welcome. I already bought an extended battery and that helped things immensely. I would be over joyed if froyo helped improve my battery life if even just by 5%. Then if gingerbread improves it another 5%, then that will be a whole hour and a half more battery life than I had when I bought the phone... just with software changes! How cool would that be?
3) Speed increase. Not that I'm complaining, because the DX is already an amazingly fast phone, so I'm not expecting any night and day improvements over the speed it runs now. I'm just really hoping that the 'OFFICIAL UPDATE' (in other words, I don't want to hear anyone say they have installed the leaked version and it didn't improve this because I'm hoping that at least part of the reason it's taking so long to roll out the official version is because they're fixing this stuff) drastically reduces, if not completely eliminates the lag I often experience with my phone. For instance, I have LauncherPro and whenever I hit the home button nothing happens... so I have to hit it again... but then it performs a double action, sending me first to the home screen, then to the screen that shows all 7 of my home screens (aaaaaarrrrrrgggggg!!!!!). So then I have to hit the home button a 3rd time to finally get it to take me to my home screen. Then there are other times when I back out of a program and get to my home screen and it freezes for 8 - 15 seconds... I can't flick through my home screens, I can't flick through my menu bar, I can't launch anything or open any widgets... it just freezes up temporarily. So, I would be over joyed if it just performed as fast as it does when it's working properly, and takes all those freezes and glitches away for me.
4) Last but not least I'm really looking forward to the enhanced features, such as the majorly improved breakdown of what apps are draining my battery. That will be SOOO useful to me.
.... no I'm not expecting to pull a brand new phone out of my pocket once the OTA updates hits me, just a slightly refined version of what I already have.