Linden Labs seem to be settling into a fairly regular cycle of maintenance + upgrade release for Second Life every Wednesday.
One of the slightly annoying things about this is that the upgrades are mandatory, and each one consists of a complete ~25Mb download. Not only that, but did you know that the upgrade installer isn’t deleted from your hard drive afterwards? Take a look in
\Documents and Settings\[your_username]\Local Settings\Temp, you’ll find some 20-25Mb files with Second Life icons – those are the installers. Better do some housekeeping.