You are not alone. I’ve actually been using 10.10 with (a slightly older version of) osxmenu since June. Installation is different, but (for the most part) everything works well.
The installer is not designed to work with the osxmenu version of Inkscape, which has a slightly different internal structure. (We will update the installer to support it when it becomes an official release.) So, you’ll need to do a manual install. Download the ZIP file from here:
Unzip the folder, and place all of the contents in:
Applications/Inkscape.app/Contents/Resources/share/inkscape/extensions/
Restart Inkscape, and you should be good to go. You may get some extra “error” dialogs when trying to print, but I think that it’s only our error reporting that has an error– all of the machine control seems to be working well.