Misha, you have stated fairly reasonable guidelines, comparable to what I have to use on other image-sites. I would bet that dial-up users would prefer images not larger than 100 K. I have been setting images to 72 dpi, and 600 pixels on the longest side, and compressing to about 8 in photoshop. This gives images which do not require scrolling on a reasonable monitor, and which are virtually always under 100 K.