We've had an infestation of whitefly on our herbs and lettuces. Absolutely smothering them. They've killed off the purslane, and they're retarding growth on all the rest. Little buggers.
I tried the brew described here of garlic, oil and soap. It seemed to work for a couple of days, but then they came back stronger than ever. Now I'm trying these yellow sticky traps. They certainly seem to be catching the bugs, but whether it'll make a dent I'm not sure. Might try combining the two techniques.
These sticky traps are really just glossy yellow cardboard with honey or some kind of sticky sugar syrup on them, so they wouldn't be hard to make. In fact, here's a howto for the project.