I just use time machine to an external hard disk via USB, and then every night an incremental backup is made to CrashPlan remote servers. At the end of the day, if you have a break-in/fire/flood - no number of mirrored disks in a NAS is going to help you.
The likelihood of the disk in your computer AND the disk in a time capsule or other basic external hard drive are pretty darn slim, so it's not of that much concern tbh to warrant a "professional grade" storage solution in your house IMO... Unless of course you're into that sort of thing.
My recommendation would be, simple time machine job to a decent external hard disk (or TC for convenience - multiple machines, portable laptops etc), and some kind of offsite backup solution over the Internet.
The likelihood of the disk in your computer AND the disk in a time capsule or other basic external hard drive are pretty darn slim, so it's not of that much concern tbh to warrant a "professional grade" storage solution in your house IMO... Unless of course you're into that sort of thing.
My recommendation would be, simple time machine job to a decent external hard disk (or TC for convenience - multiple machines, portable laptops etc), and some kind of offsite backup solution over the Internet.