Let's talk SRS

It's been brought up here and there, but have we had a specific thread about it? Probably, but I can't remember seeing one, so I'll make one now.

Seriously, why aren't you using Spaced Repetition? I keep seeing all these comments about "I study each lesson this much, but then I forget half of the words" and I can't help thinking: "Why?" It seems to me to be a terrible waste of time to learn words and then forget them. Then you have to learn them again! And then maybe forget them once more. Isn't that annoying? It sounds very annoying to me.

So why aren't you using SRS?