Ah, now THAT's what I liked about moving to OS X
I found Omnigraffle to be several miles better than Visio, and as it reads/writes Visio files I can do things better.
I moved off Windows because it started to piss me off, but Linux didn't cover my needs (complex reasons, and I've been using various shaded of Linux since Slackware came on floppies). So I got a Macbook, which runs WinXP and Kubuntu under Paralles, and then I discovered Omnigraffle.
That alone was almost worth changing to Mac for (there's a lot more). I'm not a fanatic (not my nature), but I've certainly become a fan - I don't care who owns it and what they wear, I need to get work done. With a Mac it's a matter of opening the laptop and working (also long battery life). *That* has value for m - that is worth paying for.
Back to topic: I bought iWorks, installed OpenOffice (tried NeoOffice, but I guess I got too used to "native" OOo) and also installed a "home user" copy of MS Office (main difference apart from price is that Entourage -OS X idea of Outlook replacement- won't talk "Exchange" to anything).
To date I have used MS Word exactly once, and that was by accident. The ONLY thing MS Office offers that has no equal yet is Outlook. Buggy and crap as it can be at times, it IS a mature product, and there is no replacement I have seen that comes close to it, on any platform. I reckon that's where MS spends its money - it is the one barbed hook into the average business user that is impossible to undo. The moment MS loses that monopoly, MS Office will effectively be history.
Not Powerpoint (ugh), not Word, not Excel, not it's-not-a-standard-but-we-sell-it-as-if-it-is OOXML format, no, Outlook. Think about it.