I would try to stay around 10' to avoid picking up excess noise with unbalanced cables. Some people will say up to 15', but for recording most people agree 10' should be max.
Matt
Good point about the noise, although I ran 55 feet of RCA at a show last night with no issues. If you use good quality shielded cables, you'll have fewer problems with distance.
Dirk
Yep. Let me also add that this is not really recommended. I needed a long run to the center of the room because I was doing a small multichannel recording (6 channels) and I thought it best to stick close to my mics, which were set up blumlein in the middle of the room. Turned out to be a wise move. Ordinarily, the long cable runs should be the balanced ones of course; my point was you have to work with what you have.
You need to find out how close you can get to the board and estimate your cable length from there. 10 feet is ideal for RCAs, but often you need more than that (at least in clubs around here). You just have to make it work for you somehow!
Dirk