While this is half tongue in cheek, this website and community may end up being the premier site that over half the world's programmers regularly attend - especially if Jeff and Joel create localized versions (with automatic translation, please).
The rep doesn't have a 1:1 correlation with experience, ability, etc. It does strongly hint at the ability to quickly comprehend and answer a variety of questions (check out the top 25 - few of them strongly specialize in any one type of question or answer). It also strongly hints at an obsession and perhaps spending more time on this site than working, but there may be a balance point with optimal rep - enough to indicate expertise, not so much to indicate wasted time.
At some point Stackoverflow may hit a critical mass where hiring managers will understand and use it as a hiring resource - checking out not only one's rep, but the types of answers and questions the potential hire posts, and seeing how their peers respond to them (comments, votes, etc).
I can't see what the tipping point would be though, assuming it exists in the future.
- At what point would you seriously consider adding a link to your SO user page in your resume?
- At what point would you seriously consider putting your rep number on the resume itself? (before you say never, first imagine a world where this is commonplace, and then work backwards to see what drastic, unimaginable changes would have to occur before you felt it was useful)
- If you knew your future employer is going to be looking at your questions and answers, would you review them in advance and consider closing/deleting/modifying anything?
- Ancillary - Reputation represents time, and time can also be represented by money. At what point will we see financial transactions involving rep? This certainly would happen before rep became a resume option.