Yes. Yahoo (and all major robots) will follow the standard. You can see a reference here: http://help.yahoo.com/l/us/yahoo/search/webcrawler/slurp-02.html
Thanks, jitendraag, for the great info. At least Yahoo's "Slurp" spider does not slurp up my copyrighted graphics like googlebot seems to have a voracious appitite for graphics to add to google's graphics directory. After working hard to create unique graphics it gets pretty annoying to have google redistribute my graphics for others to download and use them from the google graphics directory. It looks like using robots.txt to keep googlebot out of my graphics folder did the trick.
I tested it once - protecting one folder in robots immediately stopped the slurp, so I'd say yes, they follow the standard.
I made a robots file and thought it was working till i tested it from MSN site to fine out I was missing things in it. So it pays to check it with MSN first.