I echo Lord of the Rings' sentiments - basically $18 is not a lot of money and, on top of a noticeable connection improvement and the word Turbo-Charged in reassuringly large letters below your hyperspeed, mint blue connection bar, you also get a warm glow knowing that, despite your natural disinclination to pay for stuff, you have actually helped with the development of a very useful product.
I haven't found files roaring into my shared folder since upgrading, but they do at least canter rather than waddle these days.
I also had a few probs with the latest version for OsX but they got schmooved out when I went to an older version. If it ain't broke...

even if you dont notice the difference limewire pro is good because its what keeps limewire basic going. making limewire takes money. if you buy it you are helping them keep limewire up and running