IFinity's free module is all I ever use anymore.
Well I better make sure I send you any beta versions first before releasing them, Chris.
Not sure if the ifinity provider is better supported that way than the core provider...
The iFinity Friendly Url Provider uses all of the core API's and integrates directly into the framework as the specified Friendly Url Provider. In this way, it always works with other modules, unless the module uses some sort of after-the-fact replacement of the Url from the Core API (and, admittedly, the core RSS feed function). Generally the only problems I need to sort out for people are the occasional obscure bug and configuration for more advanced setups, such as running sites with no extensions along with modules that use different handlers and their own rewriting schemes. It's true that some modules have shown to be incompatible, but the provider allows for page-by-page human friendly exclusion, whereas the standard HumanFriendly mode is either on or off for the whole install.
As for the OP : the biggest weakness has been the standard skins and layout, and the standard Solpart menu. IMO these have far more detrimental effect than a couple of Tab Id's in the URL. Other weaknesses include the lack of a 'preferred' portal alias (all aliases are considered equal) and the myriad of 'accepted' url formats that lead to duplicate content for many.
However, I always finish a post like this with : remember that not all websites are SEO focused. Some are intranets, some are private sites, some people just don't care. It's good to keep SEO in mind in terms of options when building core functionality, but it shouldn't be the only factor taken into consideration. If people are focused on SEO the tools and knowledge are there to help them.