According to Brian Johnson, Service Pack 2 is now available via Windows Update. If you’ve been waiting, this is your opportunity. Unlike the full download, the Windows Update version is tailored to your Windows version. It’s still large, but it is considerably smaller than the full download.
Update: I just checked on my unpatched test system and WU is still not showing availability of SP2. It is available via Automatic Updates, however. I’ll keep you posted.