My quick, undetailed, and unresearched reviews (more "oppinions," really):
Emaule: nice all-around program, and I am very impressed with the way that I can search for almost anything and get not one, but a hundred responses.
Not so impressive is the way that only one out of these 100 will actually download when I click the download button, for reasons I as yet fail to understand. And the download speed is notable in its lack of, er, anything even approaching speed.
Kazaalite: who doesn't love Kazaa? Stupid question. Okay, who doesn't love Kazaa without all of its fucking ads? Better question. And all the bundled utilities that come with it are nice. ...Though I can't get fucking Proto Wall to work damnit iiiargh my technological foo has done been challenged!
WinMX: ...Better for music than anything else, really, but it is quite good at finding music. I find a lot more complete albums on it than I do on Kazaa, and the interface is quite nice. Notably less nice is the way it delights in eating up 97% of your bandwidth to download files at approximately the speed it takes for a quadroplegic to get away from Bulls-eye if you don't immediately, IMMEDIATELY! minimize it to the system tray, at which point you are limmited to only the sources you have found at that moment. Oh, before I forget:
http://www.msaxon.net/quickmix
Makes this program muuuuch better. Only works with 3.31, but there's nothing in the newer versions except chatting support which, let's be frank here, no one gives a damn about.
Imesh: I haven't had much experience with this. It's an okay interface, although its tendency to make my system perform like a drunken muel while it's on is, ah, somewhat undesirable. One thing I did notice is that you have a good tendency to find somewhat rare stuff through it. However, as I said, I don't have much experience with it because, quite frankly, the program is loaded down with more spyware than... er... something really really loaded down with spyware? That you download! FROM THE INTERNET! ...Okay, I really lost that one.
Lime Wire: interface sucks. No, seriously. I can't even use the program. As such, I can't comment on its abilities, though friends tend to find whatever they're looking for when they use it on my computer. One thing I have to say, and this goes for a *lot* of programs:
What the fuck is your problem? What, do you hotshot developers just find standard goddamned windows controls to be too mundane for oyu or something? Fucking Real Networks, oo look at us! Fuck Install Sheild, every loser in his mom's basement can use install shield! Let's make a totally new install program--and let's have it use only pictures! ONLY PICTURES! You go to click the next button or some shit but... it's a picture! Of an arrow! An arrow picture leading oyu onwards! Oh how clever we are! What the shit, oyu people? It's a fucking installation program! Nobody cares how gods-damned cynimatically pretty your fucking install program is! We just want to, say, install the fucking program! There's absolutely no reason whatsoever to go around tooling with already well-established standards just because you don't think it looks pretty enough. Fucking cock smokers.