Dave Hyatt made a post on his blog that describes a timer that Safari uses before it starts displaying any content. Supposedly the algorithm will be changed with the next release of Safari, but for now, you can still decrease the timer by setting a variable in Safari's preferences file.
Open Safari's preferences file at ~/Library -> Preferences -> com.apple.Safari.plist in a text editor and add these two lines somewhere inside the <dict> tag:
<key>WebKitInitialTimedLayoutDelay</key>
<real>0.25</real>
The default value is 1.0. Lowering the value will decrease the time Safari waits to render. Some side effects may be flashing page content as it loads, but it definitely feels faster.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20040516220739506