The winner is...
Wait ... what? A draw?
In the past, this has been where the Mac has won, and more than once. It seems that this time around the combination of Windows 7, and the bundling of Windows Live Essentials and Office 2007 Home and Student has helped Dell fight back on more than the usual platform of price, support and connectability.
Of course, while each laptop has won four rounds apiece here, it's never that simple. More often than not, people fall into either the OS X or Windows camp, and the result for them will be predetermined no matter what the other camp says — precious few are platform agnostic.
The Dell has eSATA, extra video ports, ExpressCard, a card reader that handles more formats, a higher capacity hard drive, price and support in its favour; the Mac fights back by running nowhere near as hot, being better designed, having better battery life, a higher quality display and better performance. It's worth noting though that you could probably buy a more powerful PC for less than the MacBook and completely remove the performance deficit — but our basis for comparison here is machines with similar hardware.
If we had to choose one or the other, we'd still opt for the Mac on the basis of user experience and battery life. You're not held back from tapping the great expanse of Windows software available either, as running Boot Camp or a virtualisation suite will give you access to what you need. Running OS X on a PC is well, a little harder, and not considered entirely kosher by certain parties with big legal wallets.
If you must buy now, the MacBook Pro 13 is well worth a look. Otherwise wait just a little longer — new Core i5 and i7 MacBooks and PCs are surely only just around the corner, and with them, the next battle...