Ok, my MIL is not that bad, but there are a few things that grate.
Please don't ask constantly if they are sleeping through the night/weaning/potty training etc etc, and when you say not yet, mention (yet again) how your DS (my DH) did everything 'on time'?
Also, please don't say, on the very rare occasion when you see DS, "Oh we haven't seen xxxxx for ages" when you only live up the road, are free all day and never ask to see him even though you know DIL has a long term and permanent illness.
When we are over your house, rare, please take the safety of my DS seriously and if I shut the kitchen door to stop him getting in the cupboards, please don't leave it open again, then sit on the sofa and let him wander off in the kitchen saying "he is ok", I have seen the bottle of asprin on the table well within reach, and yes while the top is child proof, there could be that one chance that FIL with the very shakey hands did not do it up properly.
That one time when you had DS in the car with the straps that were not done up properly (and my PFB was weeks old and I was already a bit about letting him go), I would like you to show that you were actually sorry about not doing the straps up properly instead of saying "oh well, we can't be expected to remember everything".
Just a few minor tips for this great book that I would love to read!