While I got this mod working too, a serious concern is that it doesn't really have much support for it any more, from what I could tell from the lack of recent responses from the creators. Another major issue is that some of the pages end up getting multiple urls, thus many addresses for the same page, which can be perceived as duplicate content to the search engine spiders (a huge no-no). Here's a perfect example...
This page has many addresses (click on each one and they'll go to the same page):
http://www.discountbabyshowerfavors.com/baby-shower-favors-c-1.html
http://www.discountbabyshowerfavors.com/baby-favors-c-1.html
http://www.discountbabyshowerfavors.com/baby-c-1.html
http://www.discountbabyshowerfavors.com/-c-1.html
Again, Google and the like might suspect you're trying to add multiple pages with the same content, something they despise immensely. In my opinion, that alone is not worth taking the chance, especially if you're going to invest a wealth of time and money into your site, ideally getting lots of people to link to your individual products/pages, only to change those URLs later on, which could have seriously negative SEO consequences...meaning, your traffic could realistically drop quicker than Paris Hilton to her knees.
Fortunately, from reading most of this thread, I learned about that magic seo urls dealy, which seems to correct all the aforementioned issues. I'm just waiting for the funds to transfer to my paypal account so I can snag this mod and subsequently install. For what it's worth, I'm not a rep for them, I'm just extremely serious about search engine optimization and have been for 11 years. It's imperative to site success that you start off with the right urls...you don't want to change them later.
Hope this info helps people. I don't want to see others invest their time only redo their URLs two years from now, which again, could really hurt. If any of you have solid programming skills, you might want to contribute to this mod and make it solid, so people won't have to ditch it later on. That could be a viable solution to these issues. Pus, since Ultimate SEO URLs already has a grip of time and effort put forth, it would be a shame to give up on it.
My 2 cent.