It's been a while since I saw a SIGSEGV, but if I remember correctly SIGSEGV can also be thrown when you try to use some memory you have freed. That kind of situation usually occurs in C++. However, in Objective-C you can send messages to null without a problem and I think that also applies to a released object, so you shouldn't see a SIGSEGV from that.

As far as autorelease pools go, remember that Cocoa provides a run loop which waits for user input then fires an event so your code can handle it. After your code is done the run loop will release any objects in the autorelease pool, then go back to waiting for user input.