Browser Page Load Performance
ejohn.org
ejohn.org
Unless you have installed Safari 4 Developer Preview (available to any body with an ADC account), your WebKit.app User-Agent string will say Safari 3.x, with a nightly revision number. The exact same revision on a system with Safari 4 will have a different string, though. So it's entirely possible to have a newer version of WebKit running in an older version of Safari, and vice versa.
I think any nightlies since the DP was released in August _ought_ to be counted as Safari 4, but some may not be for this reason.