On most papers it is far easier to coordinate your efforts by email than it is to learn svn or whatever. But I think the best is yet to come and it will be part of the class of tools being pioneered by scribtex.com verbosus.com and docs.latexlab.org. Take any of these and add -ftp or similarly convenient uploading, -some kind of guarantee of relative security/privacy, -inline preview like auctex and finally (fingers crossed), -compile with server or local TeX installations -offline mode. Those things combined will be very compelling with the added bonus of not having to install anything.