In its defence, I find it's a very convenient time to get things like water and earplugs delivered.

If the purser woke you up pre-take off, I think that's acceptable as one should be awake for the safety briefings etc. etc., and shouldn't be too much of an issue - I find the easiest thing is to cut them off politely and say hello etc. etc.

If post take-off, then a big no-no, imho; that said, I am rarely woken up to be given the spiel once in the air.