You're asking the wrong question Ben.
You need to decide what editing package you are going to use before even thinking of whether Mac or PC is the way to go. Now if you want to use Final Cut, you have to use a Mac, if using Avid or Premiere Mac or PC will be fine. If using Vegas then you need a PC.
Both Premiere and Avid are a somewhat clumsy in usage and Final Cut really pulled the rug from underneath Avid's editing domination by producing a much more elegant + easier editing package, but still very powerful. However Vegas is even easier easy to use and very powerful too. It also has the best sound facilities of any editor. Vegas was originally designed by a sound company, Sonic Foundry, which also produced the excellent Acid and Sound Forge before Sony bought them all up. Sound is extremely important to the filmmaking processs and the easiest way to make something look cheap and nasty is to get the sound wrong. Good sound and iffy picture is fine, that's stylish. Crappy sound and beautiful picture is always shite and why dubbed films are so awful.
In addition there's Final Cut Express and cheaper versions of Premier and Vegas to play with, plus there's Pinnacle [now owned by Avid I think], another PC programme which some people really like.
Do not be seduced by all the fancy transitons and such like, 99% of editing is straight cuts and dissolves. So ease of getting clips onto timeline and subsequent tweaking of length with them is the most important aspect. With Final Cut Pro you can drag different video types [DV, HDV, HD..] onto timeline without having to convert them all first to the project's settings.
I gave a producer a trial copy of Vegas to play with as he was a experienced Premiere user. He tried Vegas out and said it took him half the time to edit the test project in in Vegas and that included installing and learning the software!
The other thing to bear in mind, editing is an very skilful job and learning how to use software is 2% of learning how to edit. You can make great movies with iMovie or the windows equivalent whose name I completely forget, if you know how to tell a story. If you don't, the editing software or the computer is irrelevent.
Walter Murch has written a couple of books that are worth reading. He's quite good at splicing!
I forsee a lot of high quality rubbish appearing as a result of the 5D as lots of photographers suddenly think they are filmmakers.
Especially those used to doing it all themselves. There's a reason for having a lot of people on film sets. The ones who already work with a crew will cope best.
We will see the odd gem, but just like everyone with a digital camera suddenly thinks they are a photographer.....
