@Mike and @Jeffro:

Certainly, using a CDN will almost always provide a benefit with respect to site speed.

However, until bandwidth usage exceeds the break-even point I referenced in my original comment, using a CDN also will almost always incur additional cost for the CDN bandwidth usage.

For example, on my shared hosting account, I have a 50GB/month bandwidth quota. Currently, I will never come anywhere close to using that much bandwidth. My site averages at best 150 uniques a day.

So, for me, using a CDN, while providing a site speed increase (though to what extent, I don't know), would also incur the cost of bandwidth. For Amazon S3, the tier-pricing is modest; for WPCDN, the cost is a minimum of $6/month.

So, even if the cost is quite modest, it is still an additional cost.

Now, what would be *really* intriguing to me would be the ability to use Amazon S3 (or another service) purely as an off-server *backup* of my website (files and DB), automated through a plugin.