How much RAM do you have?
How much free space on your hard drive?
If Safari is getting very slow:
(Presumably you regularly empty your Safari cache by deleting the following file:
Home/Library/Caches/com.apple.Safari/cache.db
and clear your History)
Adding Open DNS codes to your Network Preferences, should give good results in terms of speed-up* as well as added security, (including anti-phishing and redirects) (Full information about Open DNS is here:
http://www.opendns.com/home-solutions and here: http://www.opendns.com/technology/opendns-vs-google-public-dns/ )
and further independent information can be read here:
http://reviews.cnet.com/8301-13727_7-57338784-263/free-dnscrypt-tool-enhances-ma c-web-security/?tag=mncol;txt
and here:
http://www.macworld.com/article/1146064/troubleshootdns.html?t=234
* as confirmed by: http://lifehacker.com/5835775/google-dns-and-opendns-users-are-getting-a-web-spe ed-boost
and Apple:
http://support.apple.com/kb/TS3408?viewlocale=en_US
but results may vary depending on where you are located.
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