I've had this problem for over a year. Probably 50% of the time that I plug in a USB device, memory usage by SystemUIServer goes insane, I've seen it get to 15Gb and it doesn't look like it would ever stop unless I killed it. I've reproduced this immediately after doing a disk erase and fresh OS X install, so absolutely no other software installed whatsoever, nothing. I've searched around the web and there are quite a lot of people reporting the same thing, but nothing from Apple it seems.
Mid 2011 iMac 27" for what it's worth, but I've seen other models and years reporting it too. Would be nice to get a solution from Apple.