Humm, a good question indeed.

I think it depends on how 'general' you are talking. If you refer to a forum where people can discuss matters relating to any area of life (business, work, life, travelling, hobbies, food/drink, entertainment, etc), then i'd say it could exist with no problems, but you might have a hard time promoting it, and the success would probably be very limited.

Now, if you were to set up a general sport forum (for many different sports), or a music forum (for all styles of music), you might have more success. I imagine it'd still be relatively hard to promote compared to a forum targetted to a very specific subject, however.

The benefit of forums targetted to a particular subject (such as Talkfreelance, and WebHostingTalk, for example) is that many experts in the field will hang out on the forums and therefor the advice people give/receive will often be more valuable.

Perhaps if you could devise some kind of system for your forum whereby you can ensure the content people post will be of value to others, you might see more success. But of course, you'd need to attract the attention of many experts from many different fields to come and post on your forum.