For years my cousin was suffering with the WIFI of his 2008-vintage MacBook. His MacBook would drop its WIFI connection every few hours (or minutes), and he'd have to manually stop and start the WIFI on his MacBook to fix it. The bad behavior made web surfing, Netflix, and anything else on-line quite unpleasant.
I tried everything to try to fix the problem. I replaced his router, tweaked OS settings, and even re-installed the OS. The on-line forums weren't particularly helpful - a lot of people had a lot of ideas how to fix it with software, but ultimately none of their suggestions worked.
So I concluded that the problem was with the MacBook's WIFI card.
Some of you might think that the MacBook has its WIFI chip soldered onto the MacBook's main board, but that's not the case - the classic MacBook uses a fairly common WIFI card. Getting access to that card isn't trivial, but if you're able to drive a dozen or so screws with care, it can be done.
I bought the replacement WIFI card on eBay. It was a standard Broadcom Mini PCI express 802.11a/b/g/n card with two antenna connections ... (a lot like this one at Amazon) and it was under $20.
I took the MacBook apart, based on the an on-line guide, removed the old WIFI card and put in the new one. I reassembled the MacBook.
We booted the MacBook, and everything came up fine. The new WIFI operates perfectly, and there were zero software changes that had to take place. No special drivers required, and performance and reliability has been better than ever. Interestingly, going into "About This Mac" feature of the Finder shows that the WIFI card type was a "Third Party" card instead of an "Airport Extreme".
If your MacBook's WIFI is persistently problematic, I suggest you think about having your WIFI card replaced.