If five Ruby on Rails sites utilize the same script.aculo.us library for effects you’ll have to download the same file(s) five times from each of the five different domains. Centralized resources such as YUI Hosting create a single download source requiring one file download regardless of the number of sites taking advantage of the YUI library.
The URLs are beautifully versioned and everything – this is very nice.
Alex thanks for the link, its good to see that they are offering a solution to the topic you/we discussed in the past https://alexking.org/blog/2006/11/13/prototype-size-concerns, now let see if they or someone else is able to do the same for other js libraries.