It's a good suggestion, and something we'll take note of. Some of the delay is also from how Facebook currently recommends you get profile data. It can take a few roundtrips to them asking for specific profile fields (some can get lumped together, but others can't). We already have a revised/improved system to minimize this in development. It's an approved method, just more complex than the recommendation.
The last few point releases have had some speed improvements, and the 3.1 release, we're going to be really focusing on the profile integration in numerous ways. I think we'll be able to squeeze some more speed out of logging in at that time. If not, we'll probably look into things like this, but it could get confusing for users... we like less buttons
Thanks for the suggestion.