Twitter clients on Windows Phone 7 must be like busses. You wait ages for one to show up, and then suddenly a pile arrive at the same time.
Mahtweets is a desktop twitter client with a UI similar to MetroTwit and which remains under active development.
The company is now a working an an Android and Windows Phone 7 client both, a multi-platform development story I hope we will see a lot more off.
Read more about the features of their desktop client, much of which we hope will make it over to their mobile software, here.