Expanding on previous...
Seeing as he is a time traveller, he hasn't before really used that to his advantage much before. In this episode I think SM has had a chance to kind of say 'Look, he's a time traveller, of course he wont be in the box long cos he can just go back in time later to set in motion the events to free himself so he comes out 1 minute after the baddies bugger off' - and he actually does it lots here, really rubbing in the 'this is what he is capable of, don't mess' aspect.
I don't recall any other episode where the doctor does this, the standard form is that any time travel is just to get them there in the first place.
I like how the series 'set up' was better handled - the bits & bobs he goes back in time to do across the episodes are more substantial interactions than just writing 'Bad Wolf' everywhere.
I also think there is a sneaky poke at the technique tho, when he does the zipping back & forth to fix stuff, he has to use the arm-thingy (Tardis being a bit slow & bulky for doing it that way), and he does say that it is a cheap & nasty way to time travel, mirroring the fact it is and a cheap & nasty contrivance to mess with the story. It's very post-modern to refer to the cheapness of the literary trick you are using at the time
i.e. - he can do this sort of messing around when he has to, but he would rather travel in style & fun in the woopy-woopy Tardis.
The remembering - yeah, not exactly rigorous science, but I kind of get the feeling that the entire companion arc was conceived around the pun 'something old, something new (Moffat specifically says in the 1st confidential thing that he redesigned the Tardis on the idea that it had old, modern & future components on the controls as the tardis would pick random items from throughout time to decorate itself with), something borrowed (ok, teary doctor explains that link), something blue'. So having realised that the saying can link to the tardis, the series is then set up so there is a wedding going to happen (also neatly avoiding the doe-eyed simpering of previous incarnations) and some way that the saying will save the day.
All in all, I think its a pretty good series arc, to me, more cohesive than recent previous ones
Anyway, that's enough gibbering twaddle from me