Thanks devman. May I know what is it that you do and your deciding factor to go for the 1 x 30"?
I have different work profiles (which is why spaces will be so cool - and Apple's implementation of them is very nice).
I do a lot of presentation and graphics work. So I'm in Keynote, Illustrator, Photoshop, and Omnigraffle.
I also do a lot of technical writing so I'm in Pages, Omnigraffle, Photoshop, and Illustrator.
I do development so I'm in xcode and IB.
Then there's general stuff - mail, safari, netnewswire.
In terms of going with just the 30, there was no single conscious factor. i.e. I didn't just decide one day. What happened was I had a PB15 and an ACD20 and I ran those dual head and it was great. Then I got a powermac with an ACD30 and I put the ACD20 on it as well and ran the powermac dual head. Over a period of time, I realised that I just wasn't using the 20. The 30 could handle all my windows and having that one surface right in front of me was just easier on the eye and felt easier to work with. And so, after a period of time, I disconnected the 20. Then after some more time I found I never needed to reconnect it and so I removed it altogether. I've been using just the 30 now for about a year.
I have a MBP17 now as my laptop and when I connect it to the ACD30, I never bother using the MBP17 screen (dual head). I ALWAYS run it lid closed and just use the ACD30.
Other people may have different needs, but this is what has worked out for me over 2-3 years.