Working Class Hero

It depends on the forum, and if what you have to say contributes in a substantially useful way. Adding constructive comments to fan-fics or fan-art in CEC to a long dormant thread would be OK. Adding comments to a long-dormant mod or fic just to say "this is cool" or "when is this getting released?", especially if the writer or modmaker haven't been online for more than a month or two, are not constructive and will generally get you in trouble. If it's a long dormant thread, it's probably better to PM the person you want to talk to about that issue.