Me too. According to everything written about "not breaking the browser back button" you should never do it. But, some of the hard core accessibility gurus are having a change of heart. Mostly in regards to spawning new windows for enlarged images.
The one major complaint with the above practice is that the enlarged images are usually no more than 10-20% larger and in some instances the same size as the one on the product page. Go figure! I've run into this myself just recently.
If you are going to spawn a new window with an image enlargement, please make the image a minimum of 600 pixels in width so I can really see an enlarged view. And, if you want to really satisfy me, give me the option to see it at 3X the original size (minimum 760px in width). If I'm buying something of significant value and there are details to be viewed, I want to really see them. Giving me something that is 10-20% larger doesn't really do the trick.
You want me to make that purchase online? Give me a picture thats worth a thousand words.