Gradients without transparency are doable in PS level 3, but we output only level 2 so far. Fixing this would require an expert in PS because level 3 differs significantly from previous levels. However, I don't think it's worth the trouble, because transparency is not possible even in level 3. It is however possible in PDF starting from version 1.4, so we better spend the same resources on supporting PDF instead. For now, the best alternative that I know of is to import Inkscape SVG into Scribus and save as PDF 1.4.
Thanks for the rapid reply!
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 guess I can render everything as png instead of pdf. (Pdftex can accept either as input.)
Is anybody working actively on direct PDF output? The inability to 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. Maybe it's just the nature of OSS: developers want to work on stuff that interests them personally, so that determines which features get added.