You don't. Sadly, Apple hasn't really updated Time Machine yet since its introduction with Leopard 1.5 years ago. Clearly, to be considered a true option, Time Machine has to evolve, offer more options etc.
In my view, it's a really good system for what it does. It's so good, in fact, that good tools like LaCie's SilverKeeper have not seen updates for 10.5, that one example is only available for 10.4 and earlier. Seems to me like the quality of Time Machine is killing off competition, which hinders progress.
Sadly, we probably won't see any feature upgrades for Time Machine soon. At least AFAIK, 10.6 doesn't bring much in that respect. And since it's considered a system feature, a big system upgrade like Snow Leopard _would_ be the place for its evolution. After 10.6 is released sometime this Summer, we'll probably have to wait another 1.5-2.0 years until another big cat arrives. Which could mean Time Machine _won't_ evolve for all that time. (Bug fixes, small stuff...)