Like Otterman, I experienced some problems in connecting my Macbook Pro to my home wireless router. I followed the workarounds he posted at his blog. Problem solved. Thanks Dude!
This worked for me:
Delete all “Preferred Network” listings then re-establish. One surprisingly effective AirPort Base station-specific fix for an inability to connect to wireless networks involves deleting all stored preferred networks, then re-establishing any used listings. Here’s the process:
1. Open System Preferences and select the “Network” pane
2. Select “AirPort” and click “Configure”
3. In the “By default, join:” pull-down menu, select “Preferred networks”
4. Delete the network(s) you regularly use from the list
5. Launch the “Keychain Access” application located in Applications/Utilities.
6. Click on the “Kind” filter at the top, and look for “AirPort network password” entries. Delete them.
7. Restart, or log out then back in.
8. Repeat steps 1-3, this time re-adding your regularly used AirPort networks to the list using the “+” button.
9. Restart or log out then back in.
Refer to alternative workarounds here.
My Right Brain 
Hi,
I’ve had problems with my macbook pro. After months of trying all sorts.. including the above.. I’ve finally narrowed it down to this:
For some reason the airport is setting the location to be US or DE or X3 or some other location. You can see this in the console logs.
As my wireless network was on channel 12 (which is ok in the UK) whenever the location was set to US, it decided that 12 was not a valid channel and would not connect. I had to turn off the airport and turn it back on and hope that the country was set to X3 or it wouldn’t connect.
I can’t find a way to manually set the country code or stop it resetting itself to other countries so I’ve changed the channel on my router to a channel between 1 and 10. As these seem to be allowed in the US then the router always looks there and connects. This is despite the fact that I’m in the UK and always have been!
Anyway, that seems to have worked.
Interestingly, when the security was turned off the country wasn’t reset and it always connected.
hope this helps someone else.