My last entry here was inspired by the possible use of sh404sef in the site we just launched (YAY!). We ultimately decided against using it for this site. Despite many great features that would make it a valuable addition to any site there were just too many issues I couldn't address in the time frame available before launch.
The initial motivating factor that made us look into it was a need to handle "404 page not found errors". Joomla 1.5 (J!15) does have the ability to handle these, but the additional facility to handle sef urls and reporting on site activity related to hack attempts and failed page access attempts are really exciting.
Unfortunately, the sef urls require specially written functions for any extensions in use on the site through a sef_ext file. On this site, we are using Virtuemart and Azrul's MyBlog, both of which are supported out of the box by sh404sef. rsGallery2, another extension we are using might be supported through an older sef_ext written for the J!10 version, but I didn't have a chance to pursue this. And from what I could tell on their forum, rsg2 isn't yet supported in J!15. Additionally, there are a couple extensions I wrote for this site in addition to JoomSuite, none of which are supported at all.