I really like my crazy articulated Ergotron arms (I have 3 x 24" + 1 x 17" MBP on my desk using 2 double ergotron arms). I would from now on always buy adjustable arms. The ideal would be an even bigger desk with 3-4 27-30" monitors and 2-3 work areas, and the ability to assign monitor to machine fairly independently (right now I have a dual-card PC on all 3 (as well as PC to HDMI 1080p projector), and mac as secondary on one, and cables for servers/other machines on the other two monitors. I usually leave 2 monitors on the PC and one on the mac laptop.

Once I upgrade the Mac to something which can drive a 2-3 externals (ideally, a new Mac Pro), it will get more complex; may need to use a matrix switch.