In fact, no longer a guess. From the horses mouth: next patch Tuesday the plan is for SP1 (in English, French, Spanish, German and Japanese) to be made available at the Microsoft download centre and an OPTION on Windows Update site. If Windows Update detects that you have one of the drivers that are known to be problematic, SP1 will not be offered (but you can still download it manually if you insist).
In mid-April SP1 will be a regular Windows Update and will download and install automatically for users who have set Update to run automatically.
Regards: tf1