I run a sony vaio fine, dont listen to these people.
Uhm.. Just because YOUR laptop works fine, doesn't mean you have ANY clue what you're talking about... A decent number of Vaio's have TI firewire chips and work with no problems. If you're not using a firewire interface, then you wouldn't be having problems anyway. Don't go around implying you can just get a PC laptop and have no worries. These days like 99% of PC laptops have garbage firewire in them and it will NOT work unless you use a USB interface, which isn't adequate for most recording work.
AFAIK most of the Mac issues have been resolved, I know Apple released a firewire update a while back that fixed most (if not all) problems. I was looking at Macbooks when I was laptop shopping, I've used (not for audio) the high end Macbook (the +$200 black version lol) and Macbook Pros at work, and they seem very nice. It was very tempting, especially after the Dell Vostro I bought didn't work out (Ricoh firewire, bleh) and I had to send it back. I ultimately ordered an ADK (the 1Q SR model), although I don't have my hands on it yet. Comparatively, the ADK came out a little cheaper than an equivalent Mac even with the discount I get through Apple at work.
If you get a PC here's what would be on my shopping list:
1) TI firewire. This is a dealbreaker.
2) Windows XP. I don't have enough expletives in my vocabulary to describe Vista. Vista is a resource hog, has lower audio performance, lots of audio interfaces and software are not compatible, not to mention all the built in DRM and bogus UAC security "improvements." Most laptop vendors don't even give you an option to choose XP anymore (or only on certain models) so watch out. Buying a Vista only laptop and trying to get XP on it can be a tricky proposition, I managed to do it with the Dell Vostro but it took quite a bit of research and digging to find compatible drivers. IT is my day job, if you're not extremely computer savvy I wouldn't recommend it.
3) Intel Core2Duo at least 2.0GHz, this is the lowest speed which gives you the 4 meg L2 cache. AMD isn't a terrible choice either (my last several desktops and my standard use laptop are AMD), but I'd recommend Intel at the moment.
4) At least 2 gigs of memory. I think 2 gigs is usually the "bang for buck" sweetspot with most vendors.
I'm a Cubase user myself. Going to be running a Focusrite Saffire Pro/26 as soon as I get my new laptop delivered
Good luck!