No one's actually answered that question to date, but the only thing different is that they changed the number from 0.39 to 0.40 and kept the same fixes/anticheat stuff from the beta 0.39. There's a resolution bug in 0.40. ASSS zones are blocked in 0.40 (unless you're sysop). And it's "suppose" to not spit out any error messages server-side. So basically 0.40 was released with more problems than 0.39, and without an actual updated subgame or ASSS server, there's no point on using the newer release. Edit: And not to mention the installer will override previous installations (resetting profile, macros, custom graphics, etc.). Also updates registry (though not that this is important to know). Oh, and when you're blocked out of ASSS zones, there's a new warning popup for it. Also, in the menu, "Help -> About", the copyright is now extended to 2007 instead of 2003.