On the off chance you're not following MU Trac, take a quick look at #980.
get_blog_option() is used to get an option from the specified blog but there's a trade off:
1. If we do it properly it's fairly slow. How slow? Read the ticket.
2. MU 2.7.1 used a hack to access the db directly but you lose the *_option filter which is quite important.
MU 2.7.1 out of the box doesn't use get_blog_option() that much, mostly for admin stuff, and registering new blogs. In MU trunk the function uses the slow but correct way. I've checked in changes to reduce the number of times it's called. Usually by switching to the new blog, calling get_option() multiple times and reverting back to the current blog. That improves things considerably.
So, do you use get_blog_option() in your plugin/theme? I'm tempted to use the slow method because it's more correct. I also plan on plastering the code with a big fat warning that the function is slow.
Speak up now or forever hold your tongue (or at least until the next major release.)