You gotta love the guys at XDA. A great team effort from users biktor_gj, jerpelea, and bin4ry has resulted in the Xperia X10 getting root capabilities. While this root currently only allows the user root access, there are custom ROMS in development as well. Until then, you can watch the X10 root video.
Congratulations to biktor_gj, jerpelea, and bin4ry!
Source: AndroidGuys, XDA-Developers