Definitely going to have to get used to pinning more music when on Wi-Fi. After enabling All Access, I burned up over 2GB of data in a week.
This alone, is the one thing I will miss about being on my grandfathered data plan at Verizon.
Yes WiFi is usually available, but there are definitely times it isn't. Monitoring data usage sounds as much fun as monitoring my checkbook. I'd rather I never ran out, and I didn't have to keep track of it.
Anyway, stock is good enough for me. There was a day when the stock SMS app would only send the first 160 characters of a message on Verizon. Any text beyond that was lost. I don't know if it was the apps fault, or Verizon's, but that's the issue that initially prompted me to look at Handcent.
Hancdent broke these messages into parts and sent them individually. It also marked each message with it's part number (e.g., 1 of 3, 2 of 3, 3 of 3). This feature is appreciated regardless of your choice of carriers, but particularly on Sprint, where it's anybody's best guess whether you'll even get your messages, let alone receive them in a coherent order. This problem has existed since the birth of Sprint and has never gone away for many.
However, there's another issue that I still hear about, and that's with the poor quality of MMS images. I believe the stock app limits images to a specific resolution and/or file size, and will adjust the image accordingly. If I'm not mistaken, most SMS apps (e.g., Chomp, Handcent, Go...) enable you to manually adjust this setting up to the maximum file size that your carriers network will accept. At least that's how it used to work. I just email my pics.