Oh yeah... If you have Compact Headers installed, you get the login/logout thing. But you have to have C.H. installed, otherwise the variable you're wanting isn't part of the variable that gets called.
And as for the registered members line, I don't think that is possible, because that is code specific to forum_summary. If you wanted, you could probably find the code in ubb_forum_summary.cgi that retrieves that number, and copy it into ubb_ssi.cgi. Then call the variable in the template file. But I don't think it's a good thing to have in the regular version, because it would be too redundant, and I'm not sure how cache-friendly this hack, or that addition to it, would be.
---Skorpion