Since reading on Daring Fireball that Spaces in 10.5.3 doesn’t switch around willy-nilly, I’ve found it invaluable. Summarizing, as of 10.5.3, Spaces can be set to not assign an application to a space by default when opened.

You’ll need to change your Spaces setting in Exposé & Spaces to turn off the old behavior and use the new behavior. Uncheck “When switching to an application, switch to a space with open windows for the application”. If you have any “Application Assignments” you’ll probably want to delete them. Then, log out and log in for the new behavior:

1. When you click on an application’s icon in the dock, it will bring the application forward, but it will not switch to a different space. You can now open a window in the current space.
2. If you click on an application in the dock and then click it again, OS X will switch you to the next space in which the application has an open, un-minimized window in.

That’s pretty useful, but I’ve recently discovered by accident another feature that I didn’t know about: you can drag windows to another space without switching to the space overview: drag the window to the side of the screen. If there’s a space on that side, OS X will switch to that space after about a second.

For example, I normally use just two spaces. If I’m in the first space, I can drag a window to the right side of the screen to switch to the second space; if I’m in the second space, I can drag a window to the left to switch to the first.

If I set up a 2x2 grid for four spaces, I can switch from space one to three by dragging a window down to the bottom of the screen; from three to four by dragging to the right; and from four up to two by dragging to the top of the screen.