Is the wording of "alt" description tags for images important for getting a good ranking in the Google Image Search? Which is better, a short or long description of the image? Is the word order important -- i.e. most important descriptive keyword first?
Most important keyword doesn't have to go first, and It is always better to do a shorter description. Hope I've helped, rep appreciated.
Honestly I think that a text link that leads to the image is the best way to go. It takes about 4-6 months to take effect, though.
yeah the Google bot is very slow to update. The alt gives some description of the image as well as whats on your page for the normal Google bot.
Yes, 'alt' tags within image obviously help you to get good ranking in the Google Image Search. We use alt tags as a Title of that image, so google bot easily understand what type of image it is?
Alt tags aren't enough. You need a keyword rich filename, keywords immediately next to the image, and if you can, a link to the image with keywords in the anchor text. Be very patient to see effects.