Being a current user (and lover) of Android but really wishing I could switch to WP7 for various reasons I can answer your questions or at least give you additional perspective. I haven't messed a lot with WP7 since it came out but I've steadily followed it, so someone correct me if I get something wrong. Things that I immediately missed (ymmv):
*Speech to text anywhere you can type, WP7 doesn't have it everywhere. Maybe they will, or maybe they'll just have it for texting and Bing voice search as they do now I don't know.
*100% Customizable home screen. Not a huge thing but it sure is nice, I've always enjoyed the "Sense" look. I think I could get over this though as I assume MS will allow the tiles to be modified more in the future (e.g. wish I could see all day calendar agenda from the home screen via a larger tile)
*Think of what apps you use every day and make sure there's an acceptable equivalent, this can be a big deal since you'll go from doing something regularly to just not having that ability. In my case there were a few apps that hadn't hit yet though many have by now.
*No custom ROMS, likely few tweaks available. Then again if stock is so awesome this is unnecessary and of course there are benefits to things being more controlled. However in Android you almost always had someone fixing something that bothered someone.
I'll add more later as they come to me. My eventual plan is to switch to WP7 for my phone and just have a nice solid reliable device, and then get an Android tablet for all my android love/tweaking. Best of both worlds.