I have used Limewire for years, and never had anything nasty off it, which my AV hasn't intercepted. Sure, if you download programs, you are opening yourself up, and viruses are extremely rife among this field, but if you simply use it for MP3s, and stick to what obviously ARE MP3s, you can't go far wrong.
As usual, it's all down to educating users how to use their PC safely, to recognise the signs of what is likely to be trouble, and, of course, to have adequate, updated security and anti-virus protection.