Mirc
Not mIRC!!!
Yeah, luckily I shot those anti-air missile launchers down some time ago, so they don't bother me.Completely the opposite - I have to complete the missions, or I feel there's a burden hanging over me. Similar to at the end of the game you can take over all the gang territories, I had to do it before leaving San Fierro again.
Other than that, I did grab the jetpack the other day and flew too near to their Area 51 - there's something nasty about being shot at with anti-air missiles when you just have a rocket-backpack on
However, I did find an EXTREMELY interesting bug while flying near the Golden Gate, as you opened my interest for that area. However, I'm afraid it only works when you didn't complete all the missions so that the bridge is still blocked.
Spoiler :
As you can see, I could actually drop my jetpack and walk on air!! (and this is not a cheat, believe me)
This happens on the northern barrier that blocks access to the bridge, but I think it only happens if the bridge is still blocked.