Yargh, I just did some research but I do not have authoritative answers!
1. From this page
http://forums.2kgames.com/forums/showthread.php?t=55176&page=58 , a person/people are claiming that some people had problems with digital versions of Dirt 2 (specifically the Direct2Drive version) and had to use a pirated ISO/nocd crack. Has anyone heard about or experienced this?
2. Some people like those here:
http://boards.straightdope.com/sdmb/showthread.php?t=532623 are saying that Direct2Drive has unlimited downloads, but limited INSTALLS...or potentially unlimited installs, but you have to somehow go to the website and use activation codes or request more. Does anyone have any definitive answer about D2D installs? Also, this page
http://www.gog.com/en/forum/general/direct2drive_drm/perm=2/ says that if you try to activate repeatedly in a short amount of time they will make you contact support.
3. This page
http://reclaimyourgame.com/content.php?498-drm-information claims that Dirt 2 has SecuROM 7.something, though it's only a disc check. I don't even know if that's involved with the digital versions, and Steam doesn't mention it so maybe the Steam version doesn't have it (though I think there may have been one or two games where Steam just doesn't tell you). Is that correct?