(First, if yours is an Intel Mac, check that Safari is not running in Rosetta, which is enough to slow it to a crawl. If you are running Snow Leopard, try running Safari in 32 bit not 64 bit. Control click the Safari icon in the Applications folder, then click: Get Info In the Get Info window click the black disclosure triangle next to General so it faces down. Select 32 bit mode)
Do you have enough RAM? Less than 1GB can cause slowness. Is your hard drive too full? Less than 15%, or 15GB, of free space can also cause slowness.
If you use a router, does it have the latest firmware installed? Safari 5 introduced 'DNS Prefetching' (Safari looks up the addresses of links on webpages and can load those pages faster) which could strain some routers or modems producing a 'latency' in page loading. This was fixed in Safari 5.0.1, but you may see a benefit from getting a faster router or modem.
Adding DNS codes to your Network Preferences, should give good results in terms of speed-up as well as added security:
If you are using a single computer: Open System Preferences/Network. Double click on your connection type, or select it in the drop-down menu, and in the box marked 'DNS Servers' add the following two numbers:
208.67.222.222
208.67.220.220
(You can also enter them if you click on Advanced and then DNS)
Sometimes reversing the order of the DNS numbers can be beneficial in cases where there is a long delay before web pages start to load, and then suddenly load at normal speed:
http://support.apple.com/kb/TS2296
If your computer is part of a network: please refer to this page:
http://www.opendns.com/start/bestpractices/#yournetwork and follow the advice given.
(An explanation of why using Open DNS is both safe and a good idea can be read here:
http://www.labnol.org/internet/tools/opendsn-what-is-opendns-why-required-2/2587 /
Wikipedia also has an interesting article about Open DNS:
http://en.wikipedia.org/wiki/OpenDNS
Whilst in System Preferences/Network you should also turn off 'IPv6' in your preference pane, as otherwise you may not get the full speed benefit (the DNS resolver will default to making SRV queries). If you want to know what IPv6 is:
This is Apple's guidance on iPv6:
http://docs.info.apple.com/article.html?path=Mac/10.5/en/8708.html
Click on Apply Now and close the window.
Restart Safari, and repair permissions.
Also, third-party add-ons created for a previous version of Safari may cause problems:
http://support.apple.com/kb/TS3230?viewlocale=en_US
If that didn't do it, then try this as well:
Empty Safari's cache (from the Safari menu), then close Safari.
Go to Home/Library/Safari and delete the following files:
form values
download.plist
Then go to Home/Library/Preferences and delete
com.apple.Safari.plist
Repair permissions (in Disk Utility).
Start up Safari again, and things should have improved.
More useful information here:
http://guides.macrumors.com/SpeedupSafari
