I've re-vegged one plant up to 7 times. (8 harvests total) Could have continued, but I grow a few different strains and easily tire of smoking the same strain(s) for extended periods.

The more times you re-veg a plant, the more you'll want side lighting (CFL's focusing on the lowest internodes on the stalk) twords the last week or so of harvest. This aids in the formation of new growth for the re-vegging process. This isn't as important for squat indica dominates, as it is for sativa dom's that get no usable light that far down the plant. :thumbsup: