Jonas Luster is correct when he notes that present-day XFN implementations don’t take time into full account:

Therein lies the problem. Change Dave to a friend, browse back nineteen posts, and—voila—he’s a friend there, as well. Weblogs are chronological, yet my blogroll generator just rewrote history.

This isn’t meant to knock XFN or the tools that generate XFN output for you; an implementation on this is something that’s hard to get right, and XFN’s still in its nascent stages. That doesn’t mean it can’t be fixed, though.