For everyone posting in this thread, please provide the following information:
1. The model of Mac and the amount of RAM in it.
2. Whether you are connecting over built-in Wi-Fi, Ethernet, or something else.
3. The model of Wi-Fi access point you are using, if any.
4. The model of (Ethernet) router you are using, if known.
5. The name of your ISP.
6. The city you are in (since ISP configurations can vary from region to region).
7. If you're using an Apple Wi-Fi access point (Airport Base Station), please note what firmware version.
If your problems seem to be specific to web browsing, also try a different browser (Firefox, Chrome, etc.) and see if the problem goes away. This will help sort out browser performance problems from lower-level networking problems.