As with most SEO advice, the goal is user-friendliness.
What's good for the user is good for the spider.
Do keep the accessibility issues in mind, and not just for people with "reader" browsers. The ALT text is what pops up in some browsers when the mouse is hovered over the image, adding extra information the user may need to make their decisions. (Some browsers respond better to a TITLE attribute.) It is also the text that is displayed while the image is loading, or if the image is not being displayed at all (i.e. text-only browsers, many PDA/cellphone browsers, browsers with images turned off).
I agree with the advice against stuffing keywords into the ALT attribute. You should use text that is either descriptive of the image (alt="Small Business Ideas Logo") or adds to its informative subtext (alt="Small Business Ideas Forum - Small Business Ideas, Issues, Resources, News and Help").
Lastly, your web page will not be "valid" unless you use an ALT attribute in every single image, so it's got that going for it.