Thank you again for your response, Timmey!
In 2.2, I'm positive I only created one version of each product photo, and I made them all 250px x 250px. Yet, in the left sidebar, when you see the recently viewed products, there is a mini-thumbnail there at 40px x 40px. On the catalog pages, the photos all appear at 125px x 125px. Are these other sized versions optimized to look good? No. But they work.
I guess 3.0 does not yet have this functionality, although Codeplex mentions that maybe it will be added at a later date.
I don't approve of your idea of adjusting the size of the image using CSS - it's not very efficient, as the page still has to load and then resize the full sized image, which could make your page weight pretty high -- but that's just my opinion as a designer.
If I am understanding the dashCommerce 3.0 beta correctly, it seems that whatever you choose to be your product picture needs to be small enough to fit on the catalog page (roughly 150px x 150px - ish) and that's what will also appear on the product page (although there can be other (larger) pictures available there....
I wonder if we can get Chris to chime in on this subject -- what did you intend here???