I've gone through a couple of iterations of methods for posting images online. Before Scrapbook started up, I hosted images on my .Mac account. I transitioned to Scrapbook pretty much as soon as it went live, but I've never had the time or energy to go back and transfer the previous photos over to it, since that would involve both a mass upload and changing the links in all my old posts. On the whole I like Scrapbook a lot, and I plan to keep using it as my main hosting service (yay permanent account).
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 from here on out starting with the results of my recent trip to Mexico. I'm going to start uploading larger images and posting previews that are about the same size as usual, but which link to bigger samples previews, which also link to even larger images. I'm thinking that 800 900 pixels along the longest dimension should work well; most monitors these days can display that horizontally or vertically, and the amount of screen real estate used is enough to see a lot more detail in an image. 800 900 pixels is still too small to really worry about copyright issues (I do publish under a Creative Commons license, and I'm totally fine with others using my work for derivative art under the conditions laid out in the license) so I won't start watermarking unless I have to. Again, I doubt I'll go back and retroactively change past posts, but from this day trip forward, if you're interested in seeing a larger version of the photo, just click on it and it should bring up the Scrapbook gallery it's in (with a bigger picture) and another click will show it "full" resolution.
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.