USB Throughput Monitor

I can't say that I find it terribly useful but if you open Windows Device Manager, scroll down to Univsersal Serial Bus Controllers, select an appropriate host controller, choose the Advanced tab, you will then see a percentage bandwidth use.

The only downside is that your computer probably has several different host devices so figuring out which one belongs to which set of USB ports can be interesting.

Like I said, it's not really all that useful but it's the only one that I've ever come across, unless you're talking about measuring usb disk read/write speeds, which you can do with something like HDTune I believe. (although not sure how reliable this is versus measuring fixed disk speeds, which is the true intended purpose of this app)

EDIT: I see HDTune now comes in two flavors, pro and free, and it looks like the free version is heavily crippled these days. Oh well, I'm sure there are other portable benchmarking tools if that is what is needed.

Windows 7 has Performance Monitor which you can set up to watch various USB parameters to include controller bytes/sec and that kinda stuff.

Darkbee: Try CrystalDiskMark instead of HDTune:

http://crystalmark.info/software/CrystalDiskMark/index-e.html