The original question is kind of a loaded question to me. As youll see in almost any thread about anything here, "it depends on ____." Haha
I have 2 identical small cabinets for clone and one is a small veg cabinet. Each is 12"x18", or 1.5 sq ft. For my little clone cabinet, i have two 23w, 1600 lumen CFLs for 10-12 small plants (3200 lumen, 46w). My small veg cabinet has just one 40w light for 1 small plant (both seem to be more than adequate for what im doing). My flower cabinet has six 23w CFL, but theyre around the perimiter of the 2' four bulb T5 (which is 96w, and around 9,000 lumens) for a total of 234w, and 18,000ish lumens (2'x3' cabinet, so 3100 lumen per sq ft, and 35w per sw ft).
As far as straight cfl for veg, i dont feel that a ton of power is needed, maybe 80w per plant for small plants up to roughly 1.5 feet tall. Having them evenly spaced and close to the plant is really important though. CFL loose a lot of their penetration as they get further away.
Sorry, i needlessly went into a lot of detail, but i wanted to know, so i dragged you all along while i figured some of it out.