The Dictionary app in Snow Leopard has a new feature that some people find quite annoying -- so annoying, in fact, that @luomat was compelled to Tweet about it: "I am ready to offer a bounty for a 'defaults write' to make 10.6's Dictionary stop opening new windows (@rgriff?) STAB STAB STABBITY STAB." 

The new feature, if you haven't noticed, is that Dictionary will open a new window each time you use the Open in Dictionary service (in the Services menu, or by Control-clicking on a word in a Services-aware application). If you look up a lot of words, this gets old really fast. Based on seeing my name in the Tweet, I took the bait, and went looking for an answer. For the first time in Snow Leopard, that means I used the hard method of finding hidden preferences. It wasn't actually all that hard, and I managed to find the fix in only a couple of minutes (thanks, arcticmac, for that well-written how-to!). 

If you'd prefer Dictionary not open a new window every time you look up a word using Services, quit Dictionary if it's running, open Terminal, and enter this command:

defaults write com.apple.Dictionary ProhibitNewWindowForRequest -bool TRUE

From now on, words looked up via Services will open in the same Dictionary window. Reverse this behavior by changing TRUE to FALSE in the above, or if you're a purist, with defaults delete com.apple.Dictionary ProhibitNewWindowForRequest. This works perfectly for me, and I'll be expecting that new Ferrari in the driveway by Friday, @luomat!