OSX Troubleshooting Links--Please add
 

Please use this thread to consolidate your useful links that have helped troubleshoot OSX problems.

The most basic steps are to restart in Safe Boot and Repair Permissions.

Mac OS X 10.2, 10.3: How to start in Safe Mode

Repairing Permissions

File System Check and Repair (fsck) more details what "Safe Boot" is doing

OS X 10.2 Jaguar Troubleshooting Written for the average intelligent user: taught me more about using OSX than anything else I read

Apple now has a very useful page for Isolating OSX issues

Connection Problems:
Check here to find out connection Test speed for uploads and downloads

Mac OS X: Troubleshooting a cable modem, DSL, or LAN Internet connection

Upgrading Router Firmware Also has a good link to check for router upgrades

NAT'ed? A very handy guide by Kurt Meinz for those sharing one IP with a number of computers, written with Gnucleus in mind.

Ports open? I test by downloading Chris' checknat.app.sit, (originally written for Acquisition) but it works when LW is running too.

[edit] Thanks to Ursula for the highlighting suggestions

for many more useful links, check out the Tips and Tricks forum