I have Cingular now for three months. I used T-Mobile for 8 years. I used to have so many deadspots around my daily commute including work and school aswell as my house. Since the switch I have had no problems with reception at all at all the spots that I used to have problems with. We didn't get Cingular until about a year ago in my area and wished they had it earlier.

PROS:
Great network with excellent reception.
Customer service is better than T-Mobiles.
Rollover minutes
Premier membership discount

CONS:
I have had handset issues with my phone W810 and got it replaced but still have the same exact problems. Read on cnet that it was a common problem with this handset.
Get charged for calling voicemail.
I have had problems with my Family Talk plan basically technical issues involving names on the caller ID. It took about 6 seperate calls to get it right.

That's all I can think of right now.