I have used Limewire for about 8 years now, and there is no computer I've had since then without it.
Limewire is a great program, but it is a shame many people use it for the worse. Limewire has a bad reputation, because many people have used this medium to release worms, viruses, trojan horses and spyware to people's computers. Note that spyware is available everyday when we use our web browser, such is the reason why internet browsers like Firefox block pop-ups; as they are the most common way spyware is installed into people's computers.
Luckily (and some people will grind their teeth when I say this) I have always used a Mac. Which is 100% immune to any spyware, virus, trojans, etc. To date I have only heard about 1 virus that was affecting Macs some years back. And I have not seen a virus in a Mac personally since 1993.
While there are many people who even though own many expensive anti-spyware and pop-up softwares, (Symantec, McAfee, etc.) they can't avoid having all sort of problems when using those programs. Security warnings for a mere internet cookie sometimes stops the busiest of users from doing their important work.
What does this have to do with Limewire? Simple, don't use Limewire in a PC. If you do, you HAVE TO know what you're doing. Most virus makers disguise the virus behind programs that you search for in Limewire, then when you open the file, you release the virus into your computer. Hoping to find the program you were looking for all you get is a goofy empty text file. Meanwhile the virus is working in your computer's files in the background.
Does anybody remember Kaazaa? Well, I haven't seen that one for a while but the same happened with Kaazaa. Security failures do not only happen with small internet applications only, something similar is happening with Microsoft Internet Explorer. The only difference is that Microsoft never ceases to create security updates for their browser, whilst Limewire's and Kaazaa's team can't do that. As versatile as those programs might be to some, the companies that create them are small businesses which lack the thousands of technicians that Microsoft has.
Bottom line, I suggest not to use Limewire unless you get a Mac OS X computer. Remember though that the Intel based Macs are equally as vulnerable, as PC are, to this type of thing.