UPDATE: Apple has now released iTunes 188.8.131.52, which resolves this issue.
Although Apple says that iTunes 9.1.1, released yesterday, “addresses issues with converting songs to 128 kbps AAC while syncing,” several users are experiencing an issue in which 128 kbps conversion occurs on every sync, meaning that several unchanged songs are needlessly converted and synchronized every time the sync process occurs, resulting in inordinately long sync times.
As described by Apple Discussion Boards poster Tones2: “I’m having this same problem with iTunes 9.1.1 and my iPhone 3GS with 128 kbps checked – it deletes all of my 5,000+ songs and re-converts them every time I sync. Um – This takes like 12 HOURS!!”
Another poster, Snipes01 writes: “Same problem here with 9.1.1 running on a Mac. Never had this with 9.1.0. All my music would convert from apple lossless to 128kbps on my iPhone just once. Now the entire playlist is converted on each sync.”
This problem may be solved by recreating your iTunes Library.
If you are experiencing a similar issue, please let us know at email@example.com.