Meh, I installed both CFWs (only one at a time of course), then realised how boring the emulators were, so I reverted back to OFW. No point in risking a ban over some emulators. Trygle12 is right on the mark though.
There was a rumour, and as far as I know, it's an assumption from a hacking team or something like that, that Sony could remotely disable PS3 systems, meaning you can't even use them offline. Something about how the PS3 connects to the internet for some checks on start-up, even if you don't connect to PSN. Then again, if you don't have a present connection, I don't see how that is possible....
Anyway, yeah, it's against their TOS, so they can ban you whenever they feel like it. It's unknown whether or not they can detect it at this stage. The thing is, GeoHot's CFW is signed and therefore, in theory, should be harder to detect, although it can run unsigned PKGs, so that could make it easier to detect. On the other hand, KaKaRoTo's CFW is unsigned but only runs signed PKGs. What we need now is signed CFW that only runs signed PKGs.... A completely pointless CFW, because it is basically just Sony's OFW with the Install Packages option visible.
Personally, I think it's safer to just stay on OFW for now. CFW is fun, but the fun doesn't last.