What's really clever about this is that the stylesheet you download and use in your browser merely imports another stylesheet on stevenf's own site, so that additional CSS rules to hide comments can be added for the immediate benefit of everyone without them having to download updates.
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.