I got 2008 because it has better Exchange support (although it's still not very good). I very rarely use any of the other products. When iWork doesn't suffice (which is very rare), I use NeoOffice.
Perhaps not, but I do. I've used both (all three if you count the Windows versions), a lot. You can love Word all you want, but I instantly took to Pages and find it far more capable for page layouts. As for half the features, who cares when 90% of the features in Word aren't used by 90% of people. There are only two things missing from Pages that Word has that I miss: mail-merge to email and document forms (which is handled very poorly on the Mac version anyway). For those I use Word. For everything else I use Pages.
Keynote blows PowerPoint away in nearly every way imaginable. The only thing I can think of that's missing from Keynote is the ability for embedded charts to update themselves. Otherwise, creating presentations takes far longer in PowerPoint due to the need to open up multiple dialogs for transitions, where everything can be handled more easily on Keynote with its inspector.
Numbers creates much more attractive looking charts, but I do admit to it being very slow, particularly in how it handles large spreadsheets (and by large, I mean anything over about 100 rows). Apple *really* needs to tackle performance before it can be a serious competitor. It also lacks database connectivity to have its charts update automatically.