Tip: Increase Internet speed by manipulating MTU size
Changing MTU setting fixes problems sending email
Knowledge Base: Setting the MTU value; Ethernet speed; Windows AFP servers
The MTU handling in OS X Mountain Lion may not work with the configuration for some Web servers, and might need to be adjusted.
Adjusting some Flash and system settings may help when Flash Web content hangs or shows choppy performance.
Troubleshooting Outlook Express for Mac OS 9: Problems cropping up with cable connections
The new MacBook Air has Wi-Fi issues -- so say owners in Apple's support community. This wouldn't be the first time that a new Apple product had Wi-Fi hiccups.
Troubleshooting Outlook Express: Workarounds for large e-mail sending problems
Apani Nortel Contivity client issues under Mac OS X 10.4.5
Yet more tips for boosting Safari's performance.