I respect uansari1 but on this point I've got to chime in.
I've been running the stock ROM, flashed the OTA ERE27 update and had worse performance from my radio and data connection. More times then not I found the N1 sitting in Edge and even GPRS mode.
So.... I unlocked the bootloader (voiding my warranty), loaded RA's recovery image, ran nandriod and did a backup, rooted the phone and loaded the new radio rom. Post #21 found here:
Since then I've noticed the phone staying in 3G way more than before and even better battery performance.
Still using the stock ROM.
As with any flashing READ READ READ and understand what's happening before you decide to jump into the deep end.....
More > N900 > N1 > Sensation > Moto Defy > Radar4G > Nexus S > One S