I like them. Primarily access to information and experience. The latter more than the former.
I'm not a particularly sociable person (so, f*** off, stop asking me to be your 'friend', you know who you are

) so I don't tend to involve myself too much in the pleasantries but I do recognise the value of forums equally as a 'bit of fun'.
The only thing I am sceptical of is their value for is the serious/political topic. Ime, there seems a reluctance by people to moderate, or word carefully, their opinions as they might when face-to-face. There seems to be a desire to stick to the guns, prove at all costs that they are right. I think with words on a forum being so open to interpretation (missing important tone and context as they do) they are easily misunderstood. I do think such debates invariably can end up as exchanges of fire rather than a desire to mediate. Plus, you don't know the background nor intentions of fellow debaters. That's not to say a useful debate can't happen, because it can, but that it's not the norm.