Interestingly a one time pad may be crackable. Its theoretical uncrackability is only true if a truly random number generator is used. Most cryptography is fine with urandom but a one time pad requires using something like radioactive decay to generate your pad.
This is one reason (among many) why it's impractical for most crypto purposes.
Assuming a flawless CSRNG, 128 bits of entropy is more than enough to withstand current attack power. It's hard to predict the future -- quantum computers employing Grover's algorithm could conceivably have 2x or more attack power per unit energy -- but 256 bits should be adequate for a long time.
It's fine to use low-grade sources of entropy like timestamps as long as we have enough of it. I might only generate a few bits of actual entropy per second when I move my mouse in somewhat predictable arcs, but if I keep at it for a while, I'll generate 256 bits of entropy eventually.
Right, but his point is that you're not really talking about an OTP anymore, but rather a stream cipher that's as strong as the RNG. It will situationally be quite secure, but not the theoretical unbreakability of an OTP.
This is one reason (among many) why it's impractical for most crypto purposes.