OK, hang on for a second... What packages does this RPM need to work? I presume it's built against the rebuilt GTKmm stack? Since those RPMs aren't available in public anywhere (well, except my download page, which I specifically don't want to make into a yum repo since it's not really supposed to be there...) I'm not so sure that providing this binary is really a good idea; the sane option in that case would be to provide the whole rebuilt stack (gtkmm, glibmm, libsigc++) until the FC3 Extras downloads are available.
Or point to the publicly available (and apt/yum compatible) stack of gtkmm24, glibmm, and libsigc++2 at NewRPMs and libgc at Dag RPMs. NewRPMs/Dag is really the only public place to get these packages at the moment (unless you're a Mandrake or PLD user).
People should have no problems building the source RPM on the Inkscape site, provided they've installed the stack with devel packages from NewRPMs/Dag. Theoretically, if users have the NewRPMs/Dag libraries installed, Turnip's Inkscape RPM should in fact work without problems. (I can confirm this later in the day.)
Until Fedora Extras goes live, NewRPMs/Dag is the only place to get these packages (and have any sort of quality assurance).
Btw, in Mandrake Cooker, the RPMs are named the same as in NewRPMs/Dag. And we should be able to reasonably expect they'll have the same names as Cooker/NewRPMs/Dag once Fedora Extras goes live, so there shouldn't be any conflicts in the future. (In PLD, libgc is called simply gc, but all the other package names are the same in PLD.)