anallawalla - 11:10 am on Mar 27, 2009 (gmt 0) I have had small, personal sites offline for days without a loss in rankings.
As a counter example, a part of our large site was down for 36 hours and a few days later while looking for causes for lower traffic for several days I noticed that about 1 million of our pages were no longer in the index. [Not suggesting the two are connected but it's all I have to go on, as I don't look at the indexed count often.] Two weeks later most of them were back in the count and traffic levels have returned to normal.
I have had small, personal sites offline for days without a loss in rankings.