I've just come across a really important bit of research on EN wiki.
User:Mr.Z-man analyzed the new accounts created in February to see how many were still editing in September.
Key findings:
Over two thirds of new accounts had still not become editors after 6 months.
Editors who start by creating articles are only about a quarter of new editors, three quarters edit existing articles. I find this credible if a little on the low side. But over ten thousand newbies created an article in February 2010, had their article deleted and ceased editing.
Editors whose articles are not deleted are over seven times more likely to remain than editors whose articles were deleted.
As one would expect, the retention rate of Article creators was much lower than of other new editors.
http://en.wikipedia.org/wiki/User:Mr.Z-man/newusers
WereSpielChequers