First, my sincere thanks to the Inkscape developers. You've developed a remarkable program in a very short time. The future ubiquity of SVG on several platforms owes a huge debt of gratitude to Inkscape and the people behind it.
I noted the recent concern about which versions of various libraries (gtkmm, etc.) Inkscape should target for maximum benefit. See "newest gtkmm needed to compile HEAD" and "train wreck...") As a Gentoo user (i.e. self-imposer of trainwrecks), I periodically compile Inkscape-cvs against very recent gtk gtkmm, cairo etc. Anything older than the latest Ubuntu seems positively fossilized to my biased point of view.
When I see mention of various cool features that developers have running in a private sandbox, I think it speaks to Inkscape's extreme need for a source repository that provides better support for branching and merging. I think Inkscape needs to migrate its source to subversion, and let the various devs maintain according to their interest: short-lived feature branches, long-lived maintenance branches, and convenient build bundles (svn:externals), to push the bleeding edge and still satisfy the slower pace of disto compatibility.
Inkscape has a primary role to play in the SVG revolution on the GNOME and KDE linux desktops; it can't afford to lag behind the recent graphics libraries on which Cairo is being developed. At the same time, Inkscape needs to build packages for distros (and platforms) in various degrees of stability and vintage.
Subversion could facilitate things the Inkscape developers are already trying to do. Using svn:externals, bundles could be maintained that would provide every conceivable combination of dependency, and a high probability of build success. A simple 'svn switch' would allow one to try out that latest cool feature mentioned one the mailing list, and come back to a safer branch without hassle if the feature isn't fully cooked.
Just my $0.02, Inkscape is an amazing program with equally admirable community effort behind it. Keep up the good work.