ONE
Building upon my Sample Workflow for CS1, let's outline a basic setup for CS 2.
First, start with a fully complete InDesign document which will probably have empty textframes for the content or filler text. The designer then needs to use the Export function from the InCopy contextual menu (right click on a textframe for Windows, Control+click for Apple) to export the story out in to the .incx format. This much is the same as CS 1, but there is one further step where this story needs to be added to an Assignment file. You can create the Assignment at the same time you export the story file or if you already have the Assignments set up, you Export that story directly to that Assignment option in the same InCopy submenu. If you just Export the stories, then you'll have to add them in to a particular Assignment in your Assignments window in InDesign by dragging them there from the Unassigned area.
From this point forward, the designer will need to use the Check In/Out options to edit the text that has been exported. If you're working in a small environment, then you don't need to worry about much else, unless you want to take advantage of the ability to Export graphics in to the .incx format as well, in which I'd recommend putting them in their own Assignment file, separate from the text-based files. If you have a lot of stories, you might want to break down your Assignments in to separate files, but I have yet to see that be required.
TWO
Once you have everything set up from the InDesign side of things including: the primary .indd Indesign file, single or multiple .inca Assignment files, and single or multiple .incx InCopy files, you're ready to proceed in to working within InCopy.
It's pretty simple really, you just open up the Assignment file in InCopy and start going about your Check In/Check Out business. If the designer makes a change to the file while an InCopy user is working on it, once the file gets saved, InCopy will ask the user to update their file to see the changes. Just be sure to use Check In/Check Out for changes. Using the Save won't save the file in the way you want it to and it's something of a shame that this function is still in there as it is very confusing to most InCopy users.
If upon opening an Assignment file, you get a warning screen about there being no Stories or Assignments and you only have the layout view to work with, then something is wrong with how everything is set up. You will want to check and make sure that all the required elements are in place and if all else fails, try to recreate the Assignment file from InDesign.
One last little nifty feature for InCopy users is to be able to Export a file from InCopy. This is something of an answer to the lack of generational edits for InCopy users because they can save out a copy of a story once they're done with it in to RTF or PDF format and be able to open that later and copy the text back in to the story. It is also useful in case they get last minute changes from a writer or need to converse with them because RTF will be a lot more portable format than a .incx file.