The whole idea of having an external hard drive connected to your laptop for hourly backups is insane! I can understand the concept may work with desktops, but who in the world hooks up an external drive to the laptop regularly? I tried to use Time Machine the other day with a USB drive, and it demanded to reformat my USB drive. I am not even sure it's possible to let Time Machine only use one partition for backups on a USB drive and use the rest of the drive for file storage, but even if this is possible, no one in their right mind are going to use Time Machine backups on an external drive regularly. Without regular backups, the chances of recovering all information after a failure are slim.
On the other hand, Time Capsule is a good idea but the implementation is completely botched up. Time Capsule should have RAID and have an option to be used both as a NAS and as a backup destination for Time Machine. In fact, Time Machine should be able to do backups on any network share, and not only on Time Capsule.
There is nothing in the Time Capsule manual that suggests that using Time Capsule as a NAS is even an option. Without RAID on Time Capsule, using it as centralized storage can lead to a bigger disaster than having files scattered among varous computers at home. The "server grade" HD in Time Capsule is a bunch of crap. When it fails, who cares if it was "server grade" or not?
How much more difficult would it be to put two 2.5" SATA drives in RAID-1 and allow two volumes -- one for Time Machine backups and the other one for centralized storage?
At this point, the whole concept of Time Machine is flawed. Hopefully, Apple will reconsider the implementation.
On my network, I will continue using a NAS with RAID and will have to use another piece of software for regular backups -- Time Machine is not gonna cut it for me.