Scribus actually didn't work on the example I tried. It didn't render the gradients correctly, and it also munged the fonts I was using (made Vera into a monospaced font).
I heard that Scribus (1) can't handle gradients whose nodes are outside the object and (2) has problems with fonts. The (2) is fixed by converting text to path before export, not sure about (1). Try to bug the Scribus guys about that.
Is anybody working actively on direct PDF output?
Not that I know of. It's an awful amount of work, and so far our plan was to lift, one day, the PDF code from Scribus and reuse it in Inkscape. Scribus' PDF is quite good.
output gradients to PS or PDF is a serious limitation that will probably be enough to prevent an awful lot of users from using Inkscape. Maybe my perceptions and priorities are different from other people's but it surprises me that people would be working on, e.g., Perl and Python extensions when a really basic feature like this is not yet implemented.
Personally, I would much prefer to have standard system-wide high-quality SVG->PDF and PS->SVG converters that we could use, without having to code them into Inkscape. Such a modular approach would be the best for everyone. The idea that every single design app must import and export all common formats is, IMHO, a harmful misconception originated on proprietary platforms where each app has to be self-sustaining and cannot count on cooperation from other programs. We can save a lot of resources by not following this model. I see no problem in having to run Inkscape files through Scribus or some other converter [1] when I need PDF, provided it is as cross-platform as we are and produces good output. And yes, I admit that myself I'm much more interested in developing innovative vector graphic abstractions and UI for them than in writing support for some foreign format.
[1] There was a talk of an SVG driver for Ghostscript - too bad it seems to have stalled, this would be the best solution for everything PS/PDF-related.