OS X was substantially better than Ubuntu at floating-point arithmetic.
Ubuntu returned to its position on top when it came to sparse matrix multiplication with SciMark 2.0.
Ubuntu 9.04 really lagged behind Mac OS X 10.5.6 when it came to the SQLite performance. It took Mac OS X 10.5.6 just 25 seconds for 12,500 SQL insertions while 110 seconds (or nearly four and a half times longer) for Ubuntu 9.04. However, as we discovered earlier this year when benchmarking the Linux 2.6.24 through 2.6.29 kernels, there is a serious performance regression that adversely affects SQLite's performance in the Linux 2.6.26 through 2.6.29 kernels. Ubuntu 9.04 is using the Linux 2.6.28 kernel and is impacted by this serious bug. Fortunately, it is corrected in the Linux 2.6.29 kernel and later, but unless manually switching to a newer kernel, users will need to wait for Ubuntu 9.10. It is really a shame that such a regression can get into a released kernel like that -- let alone three kernel releases -- but they should have been using the Phoronix Test Suite :). SQLite is very important for Mozilla Firefox and other desktop applications.