I earn my living developing web applications for large corporations. (I say this merely to qualify the following statesment that I make)
I use both PC and Mac to develop on. (OK also 'nix)
Except for BBEdit, I use only applications that will run on both systems. (UltraDev, Fireworks CodeWarrior etc) TexptPad is a reasonable Windoze alternative.
Productivity wise I find there is no difference between a PC or a Mac.
In fact, the Windoze OS has some neat features that I wish Apple would implement.
But more importantly, I believe that any web organization that does not check their work on Mac, PC and Linux is kidding themselves. (let alone checking between IE / netscape etc)
For this very reason the organization you are going to work with should at least have a Mac to check their work on. (Obviously this should be your Mac
)
I use a Mac from preference because I like the interface look and feel. I doubt I could justify the advantages over the PC for the work I do.
Sadly, many mainstream web companies write stuff for deployment on Windoze servers. This generally implies asp and SQL Server etc. Trust me, it easier to write asp on a windoze box.
All the best with your new job anway
. I hope you get your Mac