I am reading “The Every Computer Performance Book” by Bob Westcott (http://www.treewhimsy.com/TECPB/Book.html)
I really like his rule #7 “Ignore everything to the right of the decimal point”
A performance model or test is never going to be an accurate representation of real life then why pretend by quoting figures to X decimal places. All this does is attempt to confuse the end user and imply a level of accuracy the is not there.
I like Scott Barbers emoticon approach of using happy,sad and neutral faces to represent performance results although I often just stick with red, green and amber (possibly a little more professional).
I will stick to the sentiment rather than letter of the rule. At the moment I have a 2 second response time target from a performance test. I think this deserves at least results reported to 1 decimal places to understand if we have a near miss or a long miss and of course standard deviation to get an idea of spread.