The first one is that everyone who had the old version of Wordament will be offered the Xbox Live version through the regular Windows Marketplace update system. It does mean you have to go through the three page tutorial on the first run, but that takes seconds (and will help all the new users immensely).
You'll spot a number of UI changes as well, with the Metro UI panorama element in use at the top level of the game, and a reworking of the statistics and word solution screens presented between each game.
And then you'll spot what's missing. Your existing Wordament user name is replaced with your Xbox Live Gamer Tag, and any existing statistics have been "zeroed" and everyone is starting again from nul points. The Wordament team have explained why in detail on their blog, but note that the scores are archived in a historical leaderboard:
I realize some might question our decision to clear all the stats. The simple fact is: there was no other choice available to us. When it came time to move our identity system from screen names to Xbox LIVE we had a significant technical and policy problem on our hands.
We discussed and prototyped solutions to merge results from screen names with gamertags but the results were not satisfactory. For instance, existing players would already have unlocked most of the achievements without ever playing. It also felt very weird to launch a newly branded Xbox LIVE title that had players with millions of points. You can trust me when I say we thought through ever solution and outcome we could conceive for weeks. We finally landed on the One Year Tournament being an acceptable way to part ties with screen names and allow every player the ability to experience the game anew.
We'll take a loser look at the Xbox Live version of Wordament soon, but for now, grab your copy via the AAWP App Directory, and enjoy!