Unless something’s changed recently, Cloudfront won’t work without S3. That said, the pricing has changed considerably since this was written.
http://aws.amazon.com/s3/#pricing

SimpleCDN’s also… well… gone now. As I indicated in the original update at the top, the comparison and pricing are outdated.

If you use too much traffic on SimpleCDN (3tb+), even if you have enough balance for it, they will kill your account, purge your files, and keep the money, which was less of a problem when there was no minimum deposit. They also have a habit of reneging on price offers, such as when they offered a pay-once store-forever deal.

Nearly every other day, I find my javascript files are not downloading from SimpleCDN which blocks rendering of my web app. Often times, the latency in downloads can be 5-7 seconds!

If they simply fixed these non-stop latency issues I’ve noticed for the past 6 months, I wouldn’t leave. But unfortunately, I’m having an extremely difficult time finding another CDN that offers Origin Pull services that isn’t insanely expensive.

I haven’t used SimpleCDN in that capacity (for streaming), so I can’t say for sure.

However, think of a mirror bucket as a “dumb file server”. It won’t do any processing tasks. All it does is serve up files. So if your streaming site is simply pointing the client’s flash/whatever viewer to an mp3 file (so that the client is actually downloading an mp3 file and it’s simply being played by the flash/whatever viewer), it should be workable. If you’re actively streaming the file on the other hand, it won’t, because a mirror bucket’s just a “dumb file server” and won’t run any scripts. It can serve files – that’s all it’ll do.

Now SimpleCDN does have streaming buckets (“Live!” buckets), but those look to be meant for video, and I doubt the price is really suitable for less-bandwidth-intensive audio streaming.

In terms of performance, when using mirror buckets, the file’s often only stored on the CDN for a period of time. So every so often, it has to re-pull the content from your site which actually takes *longer* than serving it yourself (after which it should be shorter until it has to re-pull again but that really depends on the CDN’s performance compared to your own).

Really, mirror buckets aren’t designed for large files. They’re better suited to multiple small static files which benefit from being distributed around the world and served locally to reduce the latency in pulling each one of them (like for a webpage with 20 jpg/gif/css files where overhead due to latency is larger than the actual time to transfer the files).

Keep in mind that if you’re looking to optimize the performance of your server, it also depends on what you mean here. If your server load is high, it’s generally due to scripts – actual file transfers take very little cpu power, and a CDN would do zilch for you here. If on the other hand the main issue is that you’re choking your bandwidth, have heavy i/o, or have an insane number of connections causing problems, looking to serve the files from elsewhere isn’t a bad solution to look into, and a CDN could be suited to the task, although there aren’t any guarantees that it’ll perform better – remember that the goal is to have gains by serving the files from an local edge cache, and when you’re talking about a large single file, there isn’t usually a lot in the way of gains to be had here.