The bars and db do jump more than most phones, but in this case I think it's really mostly that the radio info needs to be properly relayed to Android since the phone sometimes reports 0 db signal yet I can make calls and use data.
After updating my iPhone 3GS with the new "fewer bars in more places" iOS 4.0.1, the Samsung reports the same number of bars or more one than the 3GS. It generally reports the same signal as the iPhone 4 running iOS 4.0.1. I wouldn't call that great, but it's not a total fail either. Still, from what the Captivate reports in bars and db, it's not quite as good at RF as the HTC Aria we recently reviewed.