I've done an entire grow with LED's. They are great, but of course only if you use the right kind. Weezard and Dreaded Hermie know where it's at. You really do have to build your own using 15W LedEngin emitters. It's quite costly to do it right, but if you build a light for around $400 it will produce plants that will grow in a 2'x2' area that are as productive as outdoor grown plants.

For any non-believers take a look at Weezard's album. He has a side by side comparison of his LED grown plant vs. his Hawaii sunshine grown plant. Proof is in the pudding. I'm not concerned with electricity costs, so I went back to HID until the price of the good LED's comes down.