Again, depends on the snail, though I'll admit I don't know alot about the different types. In my area all they sell are mystery snails, but if I want to go for a bit of a drive, That Pet Place is 45 mins away; and they sell nerites. I don't think either one harms live plants (though don't quote me on that without researching it).
There are others I know even less about, such as malaysian trumpet snails. These are good for keeping sand beds stirred, but that's where my knowledge ends lol. I've never kept any of them, but find them fascinating.
I have a yellow mystery snail. He/she seems to love skirting along my live plants, but does not seem to do any damage to them... I read they eat the dead/decaying plant parts so help to clean things up a bit. But, I don't think that little snail (although, a big snail, but comparatively speaking) will do much cleanup in a large tank with lots of plants.
Dragon, my oldest tank is a few yrs... well... not true... I had it shut down for awhile. But the gravel stayed wet..... I don't know. I guess my oldest tank is no more than 5-6 months old.
edit: Oh, and I did look at that website before but could not find an exact match. I posted pics of my oddball algae on this thread before. i will show you.
Lol, copper, I'm with you, I already have enough tanks to fill :D when my platy fry are grown I'm putting Diablo with them and getting a Dwarf Puffer for his 5 :) and in stocking my 29 with some type of danio, then after it cycles 5 Kuhli Loaches, and then an ABF around Christmas :D