I love my desktop, especially for work/programming. I have three 22" Acer monitors that I can have Outlook/Word/Excel, Visual Studio, SQL Server Management Studio open at the same time, all visible to me. I also like my natural keyboard, it is much easier for me to type and I imagine that I have cut back a lot of potential Repetitive Stress Syndrome. Also, when I am at my desk working, psychologically, I feel more responsible and get more done.
I also dig my shiny new laptop, a Dell XPS17 I just got a month ago, it's got a honkin' 9cell battery, 17" widescreen, and I use that at the gaming table, on a side folding tray. It's great for my PDFs and my 4e Combat manager software. (though I still like my table space in front of me to be a traditional DM screen, with paper notes and dice.

) I couldn't imagine being as productive on my laptop for work though.
I also like my Droid X phone. A slightly bigger screen than my old iPhone (which was OK, but I prefer the Android OS) and I use that for when I am at the shopping/grocery store, need to check a bank balance, Yelp a cool new restaurant or check into FourSquared, etc. Oh and as a phone too.
So yes, they all have their purposes.