Safari has a nice feature to zoom in (or out) on a webpage, which is great for large monitors. Unfortunately, you're not able to set a default zoom level for new pages. CSS hacks exist, but zooming via CSS doesn't seem to work as well as the native zoom function in Safari. The AppleScript in this hint zooms in on any new web page using Safari's own zoom function.
The script is quite a hack -- it checks every tenth of a second to see if the currently active tab isn't zoomed in. If it's not zoomed in, the script activates the corresponding keyboard shortcuts to zoom the page. You can edit the script to change how often the zoom-check should be made, and what level of zoom should be made.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20100117104428919