I think that each user should have the same user on each of the SO related sites. I'm very active in SO and have some activity in ServerFault and I don't need separate statistics for every site - just a single "meta user".
SO / SF reputation scores are measuring different things, because they have different topic focus (programming vs. sysadmin). Super User reputation is also measuring something different.
And so is participation here, technically.
We can see the desire to sync the contents of your profile (website, email, about me, etc), but not the reputation score.
I would really like to have a single place where I can point to, that has the rep points for all of my accounts.
I have attempted adding the flair from ServerFault to my StackOverflow bio page.
Having it on this site would make slightly more sense than on the other sites.
Your ID should be global, but your reputation, badges and even bio should be unique to each site. The default would be to have the same bio as the first entered, but you should be allowed to override it for each site.
Personally, I think the reputation for each site should remain separate. However, let it be pointed out that having high rep on Stackoverflow doesn't mean you know a lot about programming in general anyway. You could just be an iPhone programming god, and know nothing about Java, C, .Net, SQL, or many other popular programming topics. They may not have actually answered any programming questions at all, but just got a lot of rep answering fluffy, subjective questions that don't have much merit. You can't really draw any opinions at all about somebody based solely on their reputation. To draw a real opinion, you actually have to look of the answers they have given. All reputation means is that you have spent enough time on the site, and put in information that has been found to be somewhat useful to someone. Remember, you get +10 for an upvote, and -2 for a downvote. So you have to try really hard, or be a real jerk, to actually have a declining score.
I don't mind the differing profiles, so long as I can log into each without having to re-register.
You might thing about putting crosslinks to the other sites on the sidebar... I know it would encourage me to jump over.
I agree with @Brad Gilbert re: a "single place" for rep info - ideally I'd like to see my ServerFault, StackOverflow, Meta and eventually SuperUser "recent activity", badges and rep on 1 screen.
I think that's another site though. Ideally it would take the form of an over-arching "network." Then the individual topic sites would be children to the larger network and cross site activity can be monitored from the parent organization's site.
That would allow new specialized sites owned by Jeff and Joel to be added fairly easily as they come online. I know Jeff was thinking this is only a trilogy, but even Star Wars got prequels.
Nope. If the accounts were shared, I think it would be a bit misleading.
I'm not very good at sys-admin stuff, so my ServerFault reputation should be lower than my programming/StackOverflow rep - and it is! (I seem to be better at "meta" than programming too, I'm currently the second-top user here, for.. some reason oO)
I'm not sure if this is supposed to go in an "answer" or a comment to Jeff's post, but here it goes:
While I see what you are saying and I really don't expect to be given reputation at serverfault for my answers on stackoverflow, as the site deals with a technical aspect I know little about, why shouldn't we get our reputation transferred to this site and to superuser? I don't know, it just seems to me like a logical thing, at the very least for this site.
One thing I would like to see shared is my list of favourites.
Flagging questions because I expect to need that answer in the fairly near future. But with multiple sites I'm likely to end back with attempts to remember the right keywords for search to find it.