Barely making it in under the buzzer before we officially enter summertime, the Xbox 360 spring update is rolling out to users this week and next. A relatively small number of will get the update this week, presumably to make sure it doesn't resulting in exploding Xboxes before it releases to everyone else next week.
A pair of tweets from Larry "Major Nelson" Hryb (via Joystiq) announced the update, but don't expect it to make any noticeable changes. Hryb says this update simply adds "behind the scenes improvements & prep for future enhancements." In other words, it's paving the way for the inevitable fall update, which is likely when we'll see the addition of actual new features like SmartGlass.