The money quote from the letter (yet to be confirmed by TUAW sources) is here:
"The MobileMe launch clearly demonstrates that we have more to learn about Internet services," Jobs says. "And learn we will. The vision of MobileMe is both exciting and ambitious, and we will press on to make it a service we are all proud of by the end of this year."
Ars also notes that MobileMe management will now be centralized under iTunes exec VP Eddy Cue, who will be leading the charge for all Apple internet services across the board. We've all been through the MobileMe ups and downs during the first weeks of the service; it's nice to know (belatedly) that Apple top brass is clued in.