Just a quick caveat on the GPS/WIFI issue. This is from my personal experience so not sure it happens to everyone who updates but read that they many people had similar problems.
My 3gs, old bootrom, 4.xx iphone was on a unlockable baseband, I didn't need the unlock but thought since I'm no longer with ATT, I may need it future. So, I updated to ipad baseband with ios 5 with an untethered jailbrake with redsnow and unlocked it with ultras0w. Great.... now I have a phone that I might be able to use with other carriers in the future sometime.
That was the good... here is the bad... I noticed that my GPS did infact lose it's signal and my wifi kept going in and out even when I'm at the same place not moving the phone at all. So, although I took the chance and upgraded to ipad baseband, I wish I didn't because I actually like having my GPS and wifi FAAR more then I thought.
Here is the ugly.... once you are on the ipad baseband, there is no going back, unless if you physically remove the chip and replace it with another chip. I've read that their was going to be a update to fix this problem about 1.5 yrs ago but till this date, there is no solution. If I'm mistaken on that, someone, please correct me. TIA.
So... there you have it.... update with a caveat and know it's not reversable.
