Maybe I can add something to the discussion. I have 4 day old MacBook Unibody. I have three previous MacBooks (1.83, 2.0, and 2.2 BlackBook), as well as an early Core Duo MBP. This is hands down the best I have had. I can't speak for the later MBP's or the Unibody MBP's (which I assume our awesome!), but in comparison to those I've had, this is outstanding.
The build is fantastic. I can't see the bottom warping (though I do recall reading a review mention that - maybe it was preproduction?). Even so, my experience with Apple notebooks is that if something is going to happen, it is going to happen early on (i.e. under warranty).
The unibody MacBooks are deceptively fast - you wouldn't think the C2D 2.26 would be quick by today's standards, but for anything short of gaming or video work, I think it is more than sufficient. I don't game and I don't do video, but I am a photographer and Lightroom is just as quick as my custom built 2.7 Core Duo with 8GB ram (only 2GB in the MacBook).
I can't comment on the HDD, but that is going to be hit or miss with any HDD. I have a WD Caviar Black in an external case that makes the occasional click or hum - but it works like a champ. I put a SSD in the MacBook and it is a match made in heaven. Doesn't make a sound, incredibly fast... just so **** expensive.
If the MacBook fits your budget and will work for your needs, there is no reason not to get one. Excellent value. If you need to do anything that will be video intensive, look to a MBP (15 or 17).