With Safari 2.0 coming with Tiger in 2005, Apple is still working on improvements in the current version of Safari. Safari 1.3 (v146) was seeded to developers today and offers several under the hood improvments.
Reports indicate primarily that speed has improved noticeably, with several CSS rendering fixes. The most notable improvement appears to be in Safari's Javascript engine.
One users' BenchJS score went from 113 seconds to 16.29 seconds from Safari 1.2.2 to 1.3 (screenshot). Meanwhile Firefox .9 scored 49.0 seconds on the same test/hardware config (1GHz PowerBook).