Fair enough. So you're saying that it's acceptable for a data storage service, which is used for storing important data, to occasionally (and silently) not sync some of that data?

(1) It's not silent. The entire event was prompted by a crash and apparent shutdown corruption. (2) It's not "occasional". It's one exceptional event reported by one user.

>Claiming that a data storage service shouldn't be used for important data is claiming that it shouldn't be used. //

Really it's just saying "we disclaim liability for any losses using this service".

Which free web services offer SLAs? Or, which product in this field is guaranteeing data integrity and retention.

If we're going down that road, "any data". If it wasn't at least a little bit important, you wouldn't have written it down in the first place.