That is exactly how I do it, although I don't do that thing with the "transform selection" or hitting ENTER. Here's what I do:
1) Click on the Rectangular Selection tool (upper left corner of toolbox.)
2) Select "Fixed Aspect Ratio" from the controller popup menu. Enter aspect ratio in boxes.
3) Make rough selection. I often will put a guide down if there's a particular cutoff point I want: selections will snap to guides if you have the appropriate preference set. Sometimes I will use two guides to define a starting corner.
4) Once selection is made, click inside and drag to get it just where I want it. Also you can use the arrow keys to move it one pixel at a time.
5) Once selection is where I want it, go to "Select" menu and hit "save selection." I usually just name the selections "crop 1," "crop 2," and so forth. This is more helpful than you might think because of the next step.
6) When I'm done making selections, I save the psd uncropped.
7) Then I load the first one, crop it, put in my (C) stamp, and do Save for Web. I do this with all the permutations, naming the JPG's appropriately, and ending each one with a number tag. The first crop of photo 4399_headshot would be 4399_headshot_1.jpg. The desaturated version would be 4399_headshow_bw_1.jpg. And so forth.
8) I then use the History palette to back up to before I did the crop, load the next selection, and repeat for each crop.
9) I use the Web Gallery automation command to make a gallery of all the JPG's. Then I browse through that when I'm looking for something. The gallery shows the filename, which tells me exactly which crop and which layers to use to recreate the image from the original psd.