Mary Jo Foley is reporting that Microsoft will release a beta of Vista SP1 in the week of July 16. According to her report this keeps a timeline intact for SP1 to be released to manufacturing in November. She reports further that SP1 is mostly about fixes than features and lists some of the following:
Improvements to Desktop Search
Performance tweaks that lessen the delays in copying and moving files.
Support for ExFat, the Windows file format for flash memory storage.
Read more here.