Hopefully this isn't sounding too picky.  I'm only telling my own experiences.

I've never had slow Renders but it's subjective to what you are trying to render and what settings you are using to accomplish your rendering goals.  Are you cranking up settings without knowing the implications or using "ultra" style settings when carefully adjusting them would be better?

My renders usually are a few minutes, maybe 20 on a heavy scene.

Never had a slow UI issue (unless it was an addon in Poser 9+) and have not experienced unresponsiveness at all.  I've been using the Pro versions since Poser 7 though.

Content issues - as others have cited, its community issues and cross-support issues with "other program" (until quite recently viewing the history of it all).  Morphs still under Poses though.  Need morphs folder.  Fiddling with zips will always be an issue because not everyone has the same thought processes on how to structure (or build) content - there's a loose standard but still lots of variety within.

Can't speak for Wings (but I've read issues on occasion).  Maybe other 3D applications are better suited to the clothing building?  If it has trouble with grouping or setting materials or whatever, there are other tools that can do that so perhaps build there and optimize for clothing use elsewhere?  Seems like a problem with the modeler of choice rather than something the needs to be fixed in Poser.

Some of the solutions could be system-based (CPU, disk, graphics card, etc) and some might just be being more flexible with regards to choices (render settings, scene load, other applications).

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