> I don't know of any other products apart from S3 that could have made our file hosting as stress free as it is.
I think you're right about that part. Better solutions don't come off the shelf. Yet. :)
> What kind of scaling problems have you had?
the system I wrote at Mozy needed to scale to PBs of space and billions of files, so it was obvious that the mysql part would be a problem.
more generally I think mogile is in a pretty narrow niche: typically either you really need a lot of space and files, like flickr or facebook or ..., in which case mogilefs doesn't cut it, or you have a smaller data set but you want random access to your files in which case mogilefs also doesn't cut it.
It's definitely a solid system, though was certainly overkill for our needs (if I could do it again, I would just use s3).