As cazgar said, don't overfeed as surplus food means surplus snails. Snails are asexual, so as long as there are two individuals, they can breed. This, as you can imagine, can cause numbers to escalate quickly, but the right amount of food should hopefully prevent this.
Just watch they don't actually eat the plants, too.
I wouldn't say snails were particularly bad news, nor are they good news.
Good: they may eat algae and may make a good clean-up crew.
Bad: they may reproduce quickly which, I have heard, can have a relatively high nitrate impact. Some species may also eat vegetation.
A few snails are good, just don't over feed your fish when you get them & you won't get overrun with snails
Oh that's good news, I'm kinda excited about finding them as I'm growing ever impatient at looking at an empty tank
What do they eat? Algae I'm guessing
Some will eat algae, but most tend to eat left over food and anything else edible they can find in the tank too. One species, known as assassin snails, will kill and consume other snails other than those of their own type (or in some cases, other snails that are much bigger). For this reason, they are often sold to rid people of 'pest snails' (I believe FF2 mentioned this too).
