If you look at it from the perspective if downloading music is illegal, well in that case, Jail's and Prisons are going to be floored with thousands of people worldwide.
It's a file sharing program, like many, it's legal. It let's you download the files you're looking for from other people and vice versa, you just need to be careful and decide weather or not you're going to allow people to access your files.
It all depends on the how the person uses the program, really. In my opinion, I don't think it's illegal if you aren't downloading the music, burning onto CD's, build a small stand near some market and sell everything at half the price the actual CD cost.
Because if you look at it from another angle, you are listening to that Artist/Musician's work, weather you payed for it or not. Sure, they worked hard on making that music, but I think most musicians today prefer getting recognized and have they're decent amount of fans instead of worrying how much money they make or takes to make they're songs. Because, let's face it, record sales when a new albums drops of a popular musician and concerts rake in a lot of money, and for some it's enough. Those who prefer to chase wealth and are only concerned of that instead of making music and having the fans enjoy it, are the kinds that complain about illegal downloading.
Personally, If I were in a band and KNOW for a fact, like most musicians today, that people download instead of buying music but they still end up listening what I made, I really wouldn't give a crap. xD
Also, emm.....Frostwire kinda sucks. :X
Anyways, I rarely use Limewire these days. I just use google to search whatever I'm looking for; weather it's music, pictures, comic books, games, programs, etc. ;P
Hehe, if you know how to type things correctly in google, you could basically find ANYTHING. xP