I'm about to purchase a Lenovo for business. I go between a mac and Dell right now. The Dell is great, but it's from 2005 and on it's last leg. I had a new dell for 6 months about a year ago for work and it was a pos.
IMO... I never bought a mac, to dam overpriced. I always just go to best buy and get a bright hi-def 17'' laptop thats fairly quick, usually like 5-600 bux. Theres no need to drop 1500-2000 for a laptop dude. Im on a G72 HP right now and love it.
I have an HP and I love it. I would suggest getting an HP from Sams Club and definitely buy their 3 year extended warranty which is only 80 bucks. I haven't had any problem with my HP thus far and I've had for over two years. I would definitely buy another HP when the time is right and maybe a windows based tablet too.