Ideally, you want multiple copies of your backups in multiple locations. This protects you from N-1 devices failing (all but 1 device). The issue with multiple-location backups is that they're typically not very easy to create. They require some sort of physical activity that you have to consciously have to do to create/update/maintain them.
No matter how bullet-proof you claim your backup strategy is, if it contains a human element it's not bullet-proof. We're lazy and forgetful, many of us are procrastinators, so 'backups' will eventually end up breaking, becoming stale, or just not get updated any longer.
To this end, your backup strategy needs to be 100% automatic. This is exactly why Time Machine was invented. Time Machine automatically creates backups for you, with no intervention from you (as I'm sure you already know).
There's tons of software products out there that manage backups, and most all of them have 1 common trait: they're automatic. You set them up, and you let them go. You don't think about it, until you need to access them.
You may say you're "against the cloud" or you're just not into it, or you don't want to rely on it, whatever. Those are all fine reasons for not relying on using "cloud" services as your primary backup destination strategy. All the arguments for bandwidth and caps are completely legitimate. However, the "cloud" is the easiest way to get data from one location to another, without physically needing to transport it yourself.
You're missing out on a very reliable set of tools by not leveraging the power of "the cloud." I understand it will take a long time to upload your data initially (and probably even moving forward if you take a lot of movies), and also a painfully long time should you ever have to RESTORE your data from the cloud. However, if you use it as a secondary backup, then both of those points are moot.
Most users don't saturate their internet connection very often, and especially not in the wee hours of morning, or while they're at work. If you schedule your backups to happen during these times, then you should experience very little pain by leveraging these services.
To summarize; having an off-site backup (or two) in conjunction with your on-site backup(s) will provide you with the most reliable backup strategy. Replacing those memories is impossible once they're lost (the torture of digital media!). It's definitely worth the extra peace of mind knowing that your backup strategy is robust, reliable, and most of all SIMPLE!