The Threaded I/O Tester was used to look at the write, random write, and read performance when dealing with 16 threads and a 64MB file. The write and random write performance was better under Snow Leopard, but the read performance had regressed ever so slightly and would likely be statistically insignificant.
The system's memory performance was looked at through Stream with the copy, scale, and add operations. The performance for these memory operations had actually dropped under Mac OS X 10.6.0 for the newer Mac Mini with DDR3 memory. The older Mac Mini came out slightly ahead in the scale and add tests, but failed to win with memory copying. Granted, this is a synthetic test.
The password-cracking program known as John The Ripper was used to analyze the MD5 and Blowfish performance. The performance here was relatively the same between Mac OS X 10.5 and 10.6.