I've got a community tank with 1 Pleco, 3 Swordtails, 3 Mickey Mouse Platties, and one very lonely neon tetra. I've also got two African Dwarf frogs in there. In my opinion, they're great--the clowns in the tank. They have next to no coordination, at least not compared to the fish. It takes them forever to figure out how to get where they want to go and they're always bumping into things or kicking off too hard and completely overshooting their target. They don't seem to run into any trouble, even with the plecostamus, though they'll often complicate his otherwise peaceful day.
The other day I threw in an algae tablet which all of my fish enjoy nibbling on. Usually the swordtails will get to it first and pick at it for a little while. When the frogs finally notice it's there, it'll take them a good two or three minutes to get to it just through simple poor coodination. When one of them finally gets to it, he stretches his whole body across the tablet, which is just a little smaller than he is, and acts as though he'll guard it with his life. If the other fish ignore him and just pull the tab out from under him, which they usually do, he'll sit there looking really pissed for a minute or so and then try to attack the fish--mind you, he's got no teeth or anything so all he ever really does is slam his nose into them which leaves the fish completely unperturbed. Froggy, however, bounces off the fish and doesn't have his wits back about him until he's several inches away from the tab. It's just funny as hell to watch. The fish seem to realize he poses them no threat because they never do more than nudge him. The only fish he's ever really bothered is the pleco.
Once, I dropped the tab in right near the plecostamus and he was clearly feeling pretty hungry that day as he just charged at the thing and started devouring it as fast as he could. The other fish kept nudging or picking at him but he just wouldn't give up his ground. Finally, froggy, who'd picked up the scent of the algae tablet about two minutes prior had to go up to the surface for a breath (they breath about once an hour and even manage to make that look comical) when he shot back down to the substrate (which they [/I]always do) he hit the pleco right in the back; it looked like he was dive-bombing him. The pleco shot off to the nearest cave he could find looking indignant as hell. Poor froggy didn't get the wafer though, he was too spun out by what had just happened. The swordtails ended up getting it for a while.
In any case, I could go on but you wouldn't get it unless you saw it in action. ADFs couldn't hurt another fish to save their lives and just end up being the aquarium's comic relief. The fish don't bother them...never that I've seen. But they bring the aquariast so much fun and amusement that they're a definite improvement on any freshwater tank.
A few things about the frog:
He's nocturnal and will only run around during the day to breath, but even that takes him a few minutes to figure out.
He can eat flake food or any other fish food that sinks to the bottom (eventually) but he seems to love algae.
He won't hurt your other fish and they seem indifferent to him.
He likes to hide.
If provided the right environment, he will sing. My frogs have never done it, but I've heard of it happening and even heard a recording.
Want a frog? I'd definitely recommend the African Dwarf.
Jason