With other MODs... it can sometimes be a hassle if you don't know PHP. If you do, it's not terribly difficult to figure out how to avoid conflict. Naturally, I can't go through every other MOD and check for incompatibilities, so if anyone wants to post or send me their experiences, I can add them to my site or something.
LLusive: Is it not showing up in just one place (viewtopic or profiles) or both? Either way, it really should be a problem with either the relevant .tpl or the php files. Though if it's affecting both, it could be a more global problem. Hard to speculate though.