I think you need to post a file so we can better understand the context / requirements.
Depending on the XL version being used and the file type used when saved (see * below) the formula you outlined would be viable for Conditional Formatting as formulae are processed as Arrays by default:
If you are using XL2007+ you should be using COUNTIFS as it's significantly more efficient.
Moreover, if you are using XL2007 it also circumvents the bug outlined below at foot of post (see * section)
* in 2007 there does appear to be a bug in terms of Array formula rules not evaluating correctly on the file being re-opened
Fixes would appear to be any one of:
1) re-apply CF upon open
2) create rules in Compatibility Mode
3) use embedded INDEX calls to remove Array nature of formula
Bookmarks