ETags were added to provide a mechanism for validating entities that is more flexible than the last-modified date, very very useful !!
Look at the 13th rule: http://developer.yahoo.com/performance/rules.html
ETags are used for conditionnal requests, not for cache validation. ETag support is the responsability of the cache consumer (i.e.: NSURLHTTPRequest) and I guess it's already implemented.
ETags were added to provide a mechanism for validating entities that is more flexible than the last-modified date, very very useful !! Look at the 13th rule: http://developer.yahoo.com/performance/rules.html