Have you tried blowing it a little bit?
I can't imagine a USB port can fill up too much with dust. You might be able to dislodge a fair bit with just a little puff of air.
Just, uh, stand back a bit and maybe close your eyes when you blow.
You don't want dust shooting back into your eyes or mouth.
And other than that, compressed air is usually recommended quite a lot.
I've never used it, but I'd like to.
I searched for it online and it's surprisingly cheap. I'll have to get around to buying a canister.
Especially seeing as how my computer broke last year due to dust-build up in the fans.
They weren't spinning, the computer kept heating up, and it blew some fuses in the back. Wasn't very nice.