I'd say the chance of getting a virus or other spyware other malware are very high using a file share program like limewire.
as there is no central server the files you download are dependant on others having the same files that you are looking for.
So providing you are not downloading any copyrighted material such as songs, movie clips or tv shows that are in the public domain and your malware programs are kept up to date then you may not have a problem.
however attempt to download copyrighted material and you are opening up a can of unknown outcome. as the people who upload may have tampered with the file you want to incorperate a virus, spyware, password stealers other nasty programs that you do not want on your system.
unrelated to this limewire problem, i had javacools spywareblaster installed on my system, and this trojan program ( i think it was this, as my system was clean before the install) added the adware entry for adultlinks to my system registry. and symantec, mcafee and a nuber of other malware scanners failed to pick it up. however the only program i now recomend to keep your system clean is from www.trendmicro.com called pc-cillin internet security.
remember that file sharing programs themselves are not inherently illegal, it is how they are used that makes them that way, and as 99% of the use on file share programmes is for the illegal use of shareing comercially available media this opens up the possibility of the uploaders and downloaders being prosecuted, fined and in some cases inprisoned.
updated.
I just read what hotrod said, to a certain extent that is true. but malware can be contained in any file format. regardless of file extension. graphic files, video files and music/ audio files can often come with malware included in them. Think about one form of what i consider malware would be DRM embedded in most comercial media files these days, however DRM is just one of the many forms of file tampering out there. with DRM embedded in a file this normally directs your media player to a website to download a licence to play the file, if that site happens to be maliciouse you could soon end up with all kinds of pop ups, password stealers, viruses, spyware you name the threat and it is possible to get infected with it, and having the most up to date definitions in your malware scanner is not always the answer remember new malware is released and discovered almost every hour or less. so just use common sense. and pay for the files you want to use, or be prepared for the consequences.