One of my sites accidently uploaded a robots.txt file that disallowed all robots. It has been up for a week and half. I discovered it today when I noticed my Google and Yahoo listings had no descriptions. The rankings are still intact and I removed the file today. Google, Yahoo, and MSN spiders are still visiting several times a day. Does anyone have any idea of how long it should take for the descriptions to return? Will the rankings suffer?

If it was only up for a short time and the spiders are always there you could have lucked out and just lost temporary descriptions.... but you could also be desribing Supplemental listings... are these for really obscure terms?

no these are pretty competitive terms, SEO related keyphrases.

answer the rest of the questions.

It all depends on the PageRank of each page. The higher your PageRank then the more quickly Google will re-visit and re-index. If you know your cache tends to update every week then you'll have to wait, at least, a week.

It all depends on the PageRank of each page. The higher your PageRank then the more quickly Google will re-visit and re-index. If you know your cache tends to update every week then you'll have to wait, at least, a week.Never heard that one before....
also check your meta tags for a revisit tag what is it set to?