Interesting preliminary survey results from Macintouch:

• Nearly 11% report sudden shutdowns, 19% "the buzz", 12% "the moo", 7% warped lid, 10% AirPort dropouts, and 11% a refusal to wake from sleep. 14% report "other" problems, with excessive heat being the leading write-in candidate.
• …nearly 5% of the MacBook/MacBook Pro models have needed motherboard replacements, 4.4% battery replacement, and nearly 5% "other" repairs. The DC Inverter Board for the display is the leading write-in for repairs, plus a large handful of complete computer replacements.
• Just six people reported a melted MagSafe connector (0.2%), with another 30 (1.0%) reporting fraying, and an additional 38 (1.3%) reporting a loose connector.

Worse than I thought. More revealing is this chart:

My biased reading is that MB/MBP buyers have 60% chance of getting a 'perfect' machine and 3-8% chance of getting a machine with enough serious problems to regret buying MB/MBP. I hope Apple improves the numbers with Merom-equiped MB/MBP.