I think the Dell Lattitude line is pretty close to IBM. I've had both and the thing I like about Dell is that they aren't so proprietary. For example, you can't just buy a Thinkpad and upgrade the hard drive. It has to be one that their BIOS will recognize or you won't be able to use that particular hard drive.
They both have great port replicators, but give the nod to Dell for external LCD's.
Also give the nod to Dell for configurability. With IBM, you're pretty much stuck with what you can find unless you want to order direct - then you're going to play the waiting game. And the wait could be longer than you like.
I've never had to send a Dell back for support. We've had a bunch of Thinkpads over the years and recently the quality has started to slip. We got 4 of them last Fall and 3 of them had to go in for service or repair within a few weeks.
However, nobody, but nobody can beat IBM's service. They are very, very good. We've actually had door-to-door repairs done in 4 days.
Pricewise, I think you'll find the Dell's cheaper and with a little better support options and configurability. And Dell's are definitely ahead of the IBM's on keeping up with technology. IBM is very slow to change. They both claim an 18 month duty cycle before they are going to make any changes to the models they have.
Hope this helps with your decision. Incidentally, check out www.thinkpads.com
and send an email to Bill Morrow for Thinkpads. He may be able to save you some money and provide a "no dead pixel" guarantee that even IBM won't give you. At least with Dell, you've got 21 days to return it "no questions asked".