Do you prefer single-click or double-click behavior for system tray icons?

Many Windows client applications can iconify themselves to the system tray instead of taking up an entry on your taskbar. I love this feature for apps that I keep around all day, because it means that I always know where to find them — they're in the system tray, stupid! The problem is that there is no consensus on how many mouse clicks it should take to de-iconify such an app from the system tray: the "Microsoft standard" seems to be double-click, while the other applications that I use are now all single-click (Nick Bradbury's excellent FeedDemon was the last to move to single-click). So here's my current situation:

Application Purpose To deiconify
Outlook 2003 Mail client Double-click
MSN Messenger v7.0 beta IM client Double-click
Maxthon v1.1 Web browser Single-click
WinAmp v5 MP3 player Single-click
FeedDemon 1.5b3 Blog browser Single-click

The inevitable result of all this confusion is that I find myself single-clicking the Outlook icon, and then staring stupidly at it for a couple of seconds expecting my mail to appear, or alternatively double-clicking the Maxthon icon, and staring stupidly at it for a couple of seconds as it appears and then iconifies itself again. So, a couple of questions for different audiences:

  • For UI geeks — is there a "standard" written down anywhere for this stuff? Maybe even some nice thick usability studies that I can whack PMs round the head with?
  • For hackers — is there some fabulous little wrapper or registry hack that makes Outlook recognize single-clicks in the system tray (or alternatively, makes everything else recognize double-clicks)?

*Of course, Raymond Chen points out that we're not meant to call it the system tray, but when Google gets almost three orders of magnitude more hits for “system tray” than for “taskbar notification area” I think the battle is lost.