PLEASE tell me someone else has had this problem, as I've been having it on FOUR different iterations of the 4.0 OS (two betas, 4.0 and 4.0.1), as well as on TWO completely different devices (my old 3GS and my 4). Okay, here we go...

I'll start from a clean restore to 4.0 (from recovery mode) and "set up as new". Immediately afterward I'll jailbreak (which at this point is obviously using I then go on to install the basics, Mobile Substrate, PreferenceLoader, Activator, SBSettings, and several other non-MS plugins/apps. At this point wi-fi will be working as normal. However, as time goes on and without any system changes on my part, things start to go downhill. First the wi-fi icon in the status bar will stop showing up most of the time, then wi-fi will start turning itself OFF (toggling the switch in settings does nothing at this point). I can reset network settings, reboot, etc. and sometimes that will make it work for a little while, but then it breaks again. Eventually the connection stops working altogether and nothing I can do will make it work again (outside of restoring). The weird thing is, sometimes wi-fi will work but the SBSettings toggle will show it as disabled.

As I said, this problem has been happening to me since I was jailbreaking the 4.0 beta on my 3GS, and it continues to happen on my iPhone 4 with the latest firmware. I cannot live without the jailbreak, but I also cannot jailbreak under these conditions. I am outside any 3G coverage area most of the time and depend on wi-fi for pretty much everything. I've done a lot of Google-ing on this problem and have had absolutely zero success finding a solution, much less finding someone who can even acknowledge this problem exists. But I know it does.