I figure a lot of you out there know how to do this and maybe just need a reminder to do it...
This is for those times when you are in VS.Net and need to look at the code for some dll that your project uses, but you just don't have the code handy and VS.Net's object browser doesn't show enough information for you. In order to make Reflector the default view/browser when you double click on a dll in the bin directory all you need to do is the following: (I am assuming you have Reflector already and know what the "Show All Files" button is)
Open some project in VS.Net that uses a dll
Go to the Solution Explorer window (Ctrl+Alt+L)
Click on the show all files button
Navigate to the bin/Debug folder
Find a dll in the folder, right-click on it and choose "Open With..."
Click the Add button and find Reflector on your system
Click the Set as Default button
That's it! Now when double click on a dll in the bin directory Reflector will open loading that dll for you so you can have a power object browser when you need it