Recently on Oz, a poster had a formula that had a bunch of IS functions wrapped in IFs:
[COLOR="blue"]=IF(ISNUMBER(cond1), cond1, IF(ISNUMBER(cond2), cond2, IF(ISNUMBER(cond3), cond3, default)))[/COLOR]
(There were more than that, but I don't like counting parens).
The IFERROR function (widely dispersed in Personal.xls files, and now standard in Excel 2007) makes this more compact (and faster) by eliminating the duplication of expressions:
[COLOR="blue"]=IFERROR(cond1, IFERROR(cond2, IFERROR(cond3, default)))[/COLOR]
A little mod to the IFERROR function makes it more compact still, and more convenient for those of us with paren dyslexia:
[COLOR="blue"]=IFERROR(cond1, cond2, cond3, default)[/COLOR]
This modified IFERROR function returns the first non-error result in an indefinite list of arguments (or the last error, if all are errors):