Safari started up lickety-split: It took under 2 seconds on my 2.4-MHz Athlon 64 system with 1GB of RAM running Vista Ultimate. On the same system, IE7 also took less than 2 seconds, but Firefox took 4 and Opera 9 took 3. On a CSS test page, Safari required 139ms on first run when the browser started up and 30ms on subsequent runs. This compared considerably well with Opera's 310ms the on start-up and 250 on subsequent runs, IE7's 420ms for both start-up and subsequent runs, and Firefox 2's 309ms and 260ms.
For testing JavaScript performance, I ran SunSpider, which takes browsers through a comprehensive battery of scripts that its makers claim addresses real-world Web-development tasks, ranging from screen drawing to encryption to text manipulation. Here Safari scored 5,835.6ms, compared with Opera's 13,874.8, Firefox's 22,277.4, and IE7's startlingly bad 151,782.6. I should note that the test is hosted by WebKit, the the open-source site that is the home of Safari's engine developers, but SunSpider is well recognized in the field and a number of testing sites use it. Finally, on the DOM 1 test from QuirksMode.org, Safari scored 33ms over 10 runs, against Firefox's 145ms, IE7's 929, and Opera's 162.
I tested memory usage on the same Vista system, loading the tabs of each browser with nine popular (and multimedia rich) Web pages at once: Apple, MSN, PCMag, CNN, Amazon, eBay, CNN, the New York Times, and ABC. After letting them sit a while so any memory optimization could take place, Safari took up 121MB, Firefox 2 used 119MB, and Internet Explorer 7 usurped 162MB. Opera nibbled just 82MB. So Safari is by no means a memory hog, though not at the top of the class. For the first full launch of the product, though, that's pretty respectable.
In a couple of days' use of the new browser, I wasn't able to crash it once. I ran it on Windows XP SP2, Vista, and Mac OS X Leopard without incident.