I'm still a BlackBerry user looking forward to BB10. But I took on my own little world tour like CrackBerry Kevin (in fact earlier than Kevin did). I got a Lumia 800, and Galaxy Note. I've already been an iOS user for years, but still i went back for a short while as well on the iphone 4.
Anyway, I actually love WP 7.5. Its a brilliant looking OS with lots of potential. I actually preferred the Lumia 800 over the 900 because of the size. Its easier to type with one hand since the width is shorter. The phone fits very nicely into the hand, and I'm able to reach all corners of the screen with ease.
In terms of typing, as mentioned above one hand typing is still pretty good. The virtual keyboard is actually quite brilliant. In fact i prefer it over iOS' other than a few weird placement of characters like the "underscore". Though in terms of text editing, the trackpad and keyboard shortcuts still works better. But i mean WP7.5 is still not too bad imo.
Emails wise i have to say BB is still better. I find it easier to manage my emails. I'm using gmail, so i set it up as an exchange account. Emails comes in pretty much instantaneously as well.
Contacts management i just use gmail contacts, so its pretty similar no matter which platform i'm on. Though if you have social networks like twitter, linkedin and facebook, you'll find that you can link accounts together with your contacts much like PlayBook OS 2.0. The social network integration is the best i've seen from any platform.
Not sure if battery life is important for you, but i still find my BB having better battery life even when doing similar tasks like emails, messaging, calls, and whatsapp. That plus having more apps on WP means having to charge daily. But still its able to last me a day at least.
There are a surprising amount of good apps and games on the WP platform. Despite not being a huge mobile gaming fan, i enjoyed Wordament very much.
With the exception of Tapatalk though. I prefer the BB version. Board Express was a little underwhelming. But i'm sure you'll find most of what you need and more on the marketplace.
Overall, there are still a bit of pieces of things i found lacking. But its the same with every platform in the market as of now, every platform has it weaknesses. Its just what you can live with, or without.
I'm sure you won't find it a big disappointment. Once you get the hang of it, its pretty good. If you want to pick up a windows phone, you wont go wrong with any of the current ones. They all run incredibly smoothly. But if you can wait, why not wait for WP8, JB, iOS 6, or maybe even BB10?