Of all the major browsers, Safari is probably the biggest pain in the ass to test with. The vast majority of people use Windows and can test their sites in Internet Explorer, Firefox and Opera pretty easily. You’ll know that a web page should look more or less the same whether you use Firefox on Windows, Linux or OS X so you won’t need to install any other operating systems. Apple don’t make Safari for any platforms besides OS X and OS X is inaccessible to most people as they don’t want to purchase a new computer to test a website.
I believe some Safari users were a bit fed up of web developers forgetting about them and created services which would allow web developers to enter a URL and get a screenshot of their site in Safari. Dan Vine’s iCapture is probably the most famous one but I’ve found that it doesn’t always work and the last time I checked, it only gives a screenshot at the top of the page so it’s useless for whole pages.
Browsercam is another nice tool which is very comprehensive. It costs but there is a free trial. The free trial doesn’t give a screenshot of the whole page; again it is useless for whole pages.
I just came across SafariTest at Snugtech. This is a fantastic tool. It can give you a screenshot of your webpage in Safari at a selection of screen sizes. Not only that, it will show the whole page rather than just the top portion of it. If you’re testing scripts, there is a fantastic VNC service.