I've also wrestled with the whole issue of copyright control and such. I don't watermark my posted images, as I find watermarks on the whole to be annoying. However, I don't want full-resolution versions of my images being printed without my consent/awareness. So, to save on space and bandwidth, I tend to re-size my images to about 450 pixels along their longest dimension. This is much too small for any practical use, but generally adequate for viewing on screen. At least, it was adequate, when my skills weren't quite as honed as they are now. As a better photographer, I'm capturing more details, be they textures, lighting, shapes, or what have you. Particularly in recent weeks, I've been finding the 450 pixel size to be too restrictive; I want to show more, larger.
As such, I'm planning on tweaking my photo posts
If anyone has suggestions for a better guideline for the "high" resolution files, I'd love to hear it and the rationale behind the suggestion. I hope to pick a new standard soon and stick with it for some time, so now's really the time to give me feedback on what you'd like to see.