I know of a few people who've encountered weird Wi-Fi problems since the OS 10.5.8 update. Now Apple has released a Macbook/Macbook Pro patch for the networking issues claimed to occur under low battery power. Hopefully things will be all better now. [Apple via Ars]
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I had the problem where you had to be plugged into AC in order to stream iTunes to an Airport Express. Lets hope this is what they're fixing.