Apple in Engineering
It is true that it depends somewhat on what engineering discipline you're interested in and probably what school you're looking at. I know at least at my school there has been a push to move away from Windows and towards Linux as much as possible. However, we're more often than not having to boot up VMWare to run Windows to use something like a Word-to-osciloscope macro. At the same time, I can tell you that as far as professional electrical and mechanical engineering apps go, Windows dominates.
In terms of MecE software, there are no 3D modelling and simulation packages available for OSX. This may be changing sometime as PTC is currently working on a Linux version of Pro/Engineer so there may be a port if the demand exists. But this may not even be an issue to you unless you are willing to spend the change necessary to build a box that will run this kind of app with ease.
As far as non-Windows electrical circuit simulation goes, it's confined largely to a few open source command line utilities that are by no means as straightforward as something freely available (for students) like PSpice. I managed to stumble on a demo of a Classic PSpice app, but it was no longer supported and quite crippled.
If you're more of a CompE type, I think you'll be quite happy with OSX. Grab yourself the (free) Developer's Toolkit from Apple and you're pretty much set. X11 support is decent now and you can login to a remote machine to run apps or compile.
One software package that has recently resumed its Apple support is MATLAB from Mathworks. You'll likely become quite familiar with this package as well as Mathematica (also for OSX). If your university has the licensing set up, you should be able to login to a machine from anywhere on campus or at home and run either of these apps through the X11 terminal.
So I guess it comes down to how you're planning on using your computer while in engineering school. If it's for coding, web, email, and word processing like most people, you'll be more than happy with an Apple. I know I am with the great Airport reception and portability of an iBook.
But be aware that you're likely going to be spending a significant amount of time with a Windows box in one of the many labs using one of the many industry-standard apps.
Good luck and don't hesitate to ask any more specifics.