I know some people will disagree, but I honestly think this extension does just what it says it will do. I've installed Joomsef on about 5 different sites and never had any issue until a week or so ago. I paid for support and true to their word, they delivered a complete solution on SUNDAY NIGHT!!! I don't care what anyone says, you cannot get champagne results with lemonade efforts and any issues with an extension as good as this will either cost you money or time. Other than just being truthful about not knowing what the problem was (to start with) I was also very impressed that for the sake of meeting a deadline, they sorted out the website issues during the weekend.
This extension is not for lazy people. Put in the effort and you'll get the reward of a site with decent SEF URLs.