Some LEDS do "WORK" it depends what your definition of "work" is. Unless you spend thousands of dollars on multipul LED setups costing thousands of dollars each ... 4 TI-SMARTLAMPS for example... You wont be able to to go from seedling or clone to veg to flower to bud to harvest with an LED.. they just are not YET strong enough for that. As for certain applications they are awesome.. A full blue LED panel that you see on ebay will nicely grow plants though the seedling stage but once you get to VEG you will need more light for sure. Also an all blue LED panel that you see on ebay will help to root clones nicely.
Other applications for LED lights are as secondary lighting, as a compliment to HPS , T5-HO, or CFL's (compact florescents) or all four at once in some cases that i know.. Throw in a UVB 10.0 and your..... wait im going off track here
Also an all green LED light allows the user to view his plants during the dark cycle because plants cannot see green light
I myself use LEDS and lots of them at that... i have a 120W LED a 90W LED and two 50W LED panels from HTGsupply.com Do i wish i had my money back? On the 120W and 90W Yes i do.. but the All blue 50W and Triband 50W panel i would keep for side lighting.. The 120W and 90W were both 3 and 4 hundred dollars and they are not even close to being worth that. i would take my money back in a second because that is way expensive for a compliment for my 250W HPS and CFL's i have
So as for your question.. Do LEDS work.. yes they work very well... it just depends what you are trying to do with them.