Today I mostly spent reading up on my manager's commitments, watching Career Model training (a set of per-level guidelines of performance), researching certifications and internal training opportunities, and finish up my mid-year.
The Mid-Year Career Discussions is a formal opportunity for you and a manager to write down how you have been doing in regards to your, and your team's goals. The commitments from the previous year's review are pulled forward, and modified to reflect changes in your environment (maybe your feature was cut, or you excelled and are working on more things), with comments explaining the changes and how you've been doing. Nothing should be a surprise, as everything should be covered in the 1-on-1s I talked about earlier. For me, I'm creating all of my commitments from scratch, since I just started.
In addition to commitments, you have the opportunity to lay out development activities that you want to pursue. This is something that the developer track appears to take more seriously than the writing track I was previously under. These can be general goals like "Become proficient in WinFX technologies," or specific "Achieve MC__ certification."
The mid-year career discussion isn't scored, but what goes in it will impact the annual review later in the year (sometime before August). The employee fills out the mid-year/annual review, then hands it over to the manager. After a bit of back-and-forth (or not, for some managers), the manager adds their comments and files it with HR. After a face-to-face discussion about the added comments, you sign off on it with HR and it becomes part of your record.
Normally it is a really big deal... it's a bit odd to be drafting one of these from scratch without composing paragraphs of performance narrative.
Since I just moved to this team, I do have to fill out a transition report. It is pretty much a Mid-Year, but designed to take place anytime in the year (this contains all the performance narrative that is missing in my mid-year). Its purpose is to assist the new manager in identifying your overall performance when it comes time to talk about compensation during the annual review. Since I moved half-way through the Microsoft year, this is an important document (as it counts for about half of my year-end score). I filled this out just before going on Christmas break, and now need to open up the dialog with my previous manager to get his input on it.