I'm betting you've got a fungus gnat problem... if you think you see "gnats," they're most likely fungus gnats, which vaguely resemble fruit flies. They don't do SEVERE damage to leaves, but just do a little munchy-munchy here and there. They can also nest in the bark and the newborns can nibble on the roots of an orchid, which isn't so good.

I have been battling fungus gnats for a while now. Neem oil didn't do anything for them. I think it's because they spend most of their time in the bark and buzzing around the plant, and not that much time actually sitting on the leaves themselves. One way to find out what you're dealing with is getting yellow "sticky traps" and setting them up around some of your plants. You can find these online. Just do a search for "yellow sticky bug trap" and you'll come up with it. There's various designs of them out there, but they all work on the same principle: bug lands on yellow sticky surface and gets stuck. Bug dies.

I have noticed a HUGE reduction in the amount of fungus gnats I've been dealing with since I've started using these yellow sticky traps. The added benefit of the traps is that you get to see whatever's munching your plants in full view once they're caught. There are some organic products out there that specifically address gnat problems... one that came highly recommended was called GoGnats. I haven't tried it myself, but I'm getting ready to!

Anyway, I recommend setting up some sticky traps, waiting to see what you catch, and then posting a pic! It'll be gross, but at least we'll be able to identify the pest (if it is indeed a flying insect of some sort).

Good luck!!

---------------- Update: Just found an even BETTER product to get rid of fungus gnats. It's called Gnatrol WDG. Do a Google search and you'll find it. You spray it on the top layer of potting media and it kills the larvae, which then in turn gets rid of the adults.