Yeah, I'm on an iBook and feel for you. The whole reason why I intentionally got the iBook (even as I knew the macbook was coming out any day), is because of size - I didn't trust that Apple would come out with anything this small soon. To me the main selling point of iBook is size - it's perfect. Smaller would be too small from the point of view of the screen... I wouldn't mind thinner, and I certainly would welcome lighter, but not a smaller screen than 12".
Thing is, if you need to carry your 'book around, every inch and every ounce count. I just find the MB unwieldy - actually kind of an uncomfortable size. The iBook seems much more proportional and aesthetically pleasing. My objection to the 12" PB was that it seemed too fragile. My iBook in it's hard case seems bulletproof... for something that I use on the go, this is important.
As to keyboard, I've tried the MB and agree - it's better than the iBook. My iBook keyboard is kind of lame... springy, spongy, key edges are sharp and are often getting caught on fingertips, sleeve of the sweater and so on. Not great. And the screen is the weakest thing on this thing - so dim. If there's one think I really wish the iBook had is a better, brighter screen.
Also, I think the MB runs a lot hotter than the iBook - another point against the original 12" PB which I'd otherwise consider. I hate the frying heat on your hands/lap, the damn fans coming on etc. - all that I associate with the 12" PB and now all intel macs, including the MB. By contrast my iBook is cool as a cucumber most of the time - even when it's doing intense video encoding for 48 hours straight!
I so much don't like the new MB and generally intel laptops, that I've just poured $345 into my iBook to get a 120GB hard drive... rather than upgrade to a new MB, I prefer to stay with the iBook and extend it's power as much as I can - I love this form factor, I love the coolness, the long battery life, the excellent WI-FI reception etc.
So am I disappointed in the intel laptops from Apple - YES. Hot, buggy, crashy, and don't run a lot of PPC software that I have.
I'll eventually buy another Apple laptop, but it'll be probably in a year or two, after they solve or at least lessen the heat problems. And maybe we'll get lucky with a nice form factor.
Meanwhile talking about product range - where's Apple's sub-Mac Pro? I'd love something that's mid-range between the mini and the pro, but without laptop components and a forced monitor like the iMac, and something that doesn't cost much more than around $1000. But that's another topic.