I've been playing around with an HTC HD7 for a few weeks now, and I'm quite disappointed at the lack of functionality of the OS. I mean it's fast, and for a few basic apps and messaging and media, etc., it's OK, but it's missing so much:

No Flash, very few applications, no custom ringtones, no cut & paste and so on.

I bought it specifically to connect it to Exchange 2010 when we install it, but even connected to Exchange 2003, for a Microsoft OS it's a dog.

It seems to me that they rushed out this crippled version just to try and get some market share out of the Christmas rush, which is a pretty stupid reason to do so.

However, there appears to be a large January update coming which will start to address some of these problems, at least that's what the URL suggests (although of course they could mean January 2012):

January Update

And other gossips suggests a much bigger update to follow not long after:

Windows Phone 7 handset owners are most likely to receive an update at the beginning of 2011, with a larger, more feature rich update coming soon after in February.
So I'd have to say at the moment, I wouldn't bother buying a WP7 phone. It's not even close to matching Android or iPhone yet.