The ?? operator was introduced to C# in 2.0 and I made a mental note to myself to use it when possible.
Recently I had to do some tinkering with good ole Request.Form and Request.QueryString and I kept trying get the neurons to connect and figure out the shorter way of doing it. I knew there was another way to do it than write all this.
And Google is no help when you have no keyword to search. This is when ReSharper came in handy and prompted to replace the above code with this succinct version.
BTW: If you are coding in VS 2008 check out the ReSharper 4.0 nightly builds, it's awesome.