For lack of a better term, it sucks. The drivers that come with these things can often be more of a resource hog and harder to remove than a Root Kit. As a rule, I won't trouble-shoot a machine running USB ethernet. I'd rather set up a token ring network instead.
I've joked that USB ethernet was a hack invented by ISPs because they didn't know how to configure a basic Windows network card, nor wanted to deal with them.
Problem is I'm not a bit fan of PCI wireless cards either. Most are just a poor PCMCIA wi-fi card strapped to a PCI interface with an antenna on the back. Still, they are better than USB Wi-Fi, or until Intel gets its new chipset on the market which is supposed to fix some of the problems with USB ethernet...I believe.
If you have a Linksys Wi-Fi router and want the best performance, then there's a better way to do this. Get a LinkSys access point of the same class as your router, plug it into your ethernet port, and put the sucker in bridge mode. It will be secure, and have better data transmission than a PCI Wi-Fi card. Usually MUCH better.