I don't think they're useless - Just not quite as good as tube lights.
I was very frustrated with the 20 watt tube that came with my 20 gallon
long aquarium, it provided just enough light to see the fish and make
any plant I added to the tank die *very* slowly, but still die.

So in an effort to get more light into the aquarium I pulled the tube
and ballast out of the light hood on my tank and cut out a piece of
alluminum sheeting for a reflector plate and mounted it inside the
hood. Then I went to Home Depot and got two screw in light sockets and
a pair of brackets to hold them. Mounted them on the inside of the hood
so they would be equally spaced over the aquarium and screwed in two
25watt screw in flourescents.

So theoretically the tank has 2.5 watts per gallon in it now. From what
I've seen though it's acting more like it has between 1.5 and 2. Still,
for a total cost of less than $30 (bulbs included) it was a heck of a
lot better than buying a new hood from the LFS. I can now keep all low
light plants and many medium light plants in an aquarium that wouldn't
support any plant life at all before the modification.

-Daniel