OK
It depends on many factors. Where you live. If you share what you download. If you share a few or many files. What kind of files. If the files are new or popular. If you are connected always. If you protect yourself or not.
The more visible you become to the organisation trying to stop file sharing, the more likely you will get sued.
If you are planning on using Limewire to download copyright material, then depending on where you live there is always a slim chance of getting caught.
This is quite impossible to answer and you still haven't said what it is you heard about downloading illegally
Here is one thread dealing with the same issue
Click on me Illegal ? use the forum search if you want more reading. Search for words like legal, illegal, RIAA, MPAA, MAFIIA, Legality etc.
If they go after you for copyright infringement then they will try and hold you liable. You can't blame limewire for making it possible to do so, even if that's what they're trying to do. They are pretty much going after all file sharing apps now