Okay, not so much the use of the CSS @import rule as much as the mechanism used to deploy the rules. I haven't seen a lot of user installable stylesheets that "phone home." Seems like an under-utilized technique.
UPDATED: Yes, I understand @import is used frequently on the web. My point being A) You don't see a lot of browser-installed stylesheets and B) the few that I've seen haven't made use of @import.
It's used all the time by many people. I use it to let affiliates skin their own sites on apps I host. Referencing a stylesheet on another server is hardly anything inventive.