Ask an important question of yourself. Do you need backup or online replica? Sound similar, but they're not the same thing.
Backup services enable you to revert to older versions of files e.g you accidentally save changes to a file, backups enable you to recover deleted files, backups enable you to permanently archive files safe in the knowledge you can recover them in the future.
Neither Dropbox, Mesh nor Mozy and many similar services in that genre are backup services. They offer online replicas of files, but they don't offer historic revisions of data - that accidental save will overwrite immediately if you're connected to Dropbox, nor support recovery of deleted data. Though Mozy may retain deleted files for ~30days - woe betide you if it takes more than 30 days to discover you deleted something.
I've used services like Mozy to store incremental and full backup sets created by backup software - that works quite successfully. But to be clear - I don't let Mozy backup my whole drive, it only syncs those backup files.