Is limewire pro illegal to use???
 

Depends on what you will be using it for. Whether you are using Pro or Basic Limewire does not make downloading stuff, otherwise illegal to download, suddenly legal. It mostly depends on the laws where you live, or at least whether you stand the chance of being sued for downloading and sharing copyright works.

Legality
 

In the US is it legal to download music from any version of Limewire, or not?

It's not illegal to use p2p sharing applications. It is not illegal to share files. Depending on your country laws however, it is most likely illegal to share copyright files. ;)

If there is a file you are seeking & you google search it & find it for sale somewhere, then it is most likely a copyright file.

Note: Buying LW Pro does not make sharing/downloading copyright files legal. :)

Thanks Lord of the Rings
 

I guess we'll choose to be safe than sorry...