Several people who own the new, unibody MacBooks and MacBook Pros are reporting trouble with the glass trackpads. Specifically, it's been failing to register clicks, seemingly at random. One user even told PC Pro, "I don't even attempt to use this machine unless I'm at a desk using a mouse."
One user sent a complaint to Steve Jobs via email, and (reportedly) received the brief reply, "Software fix coming soon." We couldn't confirm that Steve himself actually sent this message, but he has responded to user emails in the past.
Personally, I've only used a new MacBook for a few hours and didn't experience any issues. We'll let you know as soon as this update becomes available.