I was drinking some V8 the other day, and I noticed that an 8 oz. serving has "twice the potassium of a banana!" Also, the stuff is pretty loaded with sodium -- even the low-salt variety. I haven't tried V8 before a workout, but it seems to have a good amount of electrolytes, if nothing else.
P.S. I tried to do a forum search because I'm sure this isn't a new idea. Unfortunately, "V8" was too short to use as a search time.