I think that the @ is a perfect way to visually demonstrate referencing a person (instead of linking to a profile.) It's pretty ubiquitous on the web now and instantly recognizable as a "mention" (facebook also employs the @ to notify a user that they're being mentioned)
Are you trying to notify the person that you are talking about them or are you trying to link readers to that person's profile? (I think the @ symbol would work in both contexts)
As a user, when I see @username and I click on it, I expect to be taken to that person's profile (presumably to check them out, add them to my friends list, etc)
Also, when I am on a site and want to mention someone, I get aggravated if I can't use @. Because it is fairly widely accepted convention, I basically expect this sort of functionality to be present. Often if it isn't, such as on an older forum, I will still just type out @username and hope that the person I am trying to talk to will see it.
Hope this helps!