So much. I've been here since 2006 and I think I've only very rarely come a cropper through advice or something suggested here. I view myself as benignly radicalised by MN feminists
. I became very informed about HRT choices and options, and was able to go to the GP armed with the correct and most up-to-date reviews and guidance, in the face of my GP's terribly outdated information and stance. I was able to read about how horribly some women suffer with an outpatient hysteroscopy without adequate pain relief, and therefore pushed to have mine under GA. I used to find the SEN pages hugely useful in the early years with my younger child, though I did find that the same sort of line was being pushed WRT autism. Perhaps it's not any more.
Random things I have bought/done because of MN: Turkish haman towels for camping and general bathroom use - so quick to dry, pack down tiny!
The MN 'flying squirrel' jumpsuit.
The MN scarf, a few moons ago.
Lagenlook linen clothing for the dumpier of stature.
My blessed mooncup.
Using Buttery in Victoria Sponges rather than all butter (makes for a much lighter, less greasy cake and you honestly cannot tell).
Making village show prize-winning Victoria Sponges thanks to a vintage thread started by Slubber.
Also thanks to her, actually buying and cooking with and loving PFB in stews etc. 
Picking random shopping lists out of trolleys and regaling my bored family with them.
Lots of weight-loss information and support (it can be a bit bewildering on the weightloss boards though).
Cat help - that brilliant enzyme spray you use if they pee somewhere bad.
My wool pillow.
Treating myself to an M&S beauty advent calendar in December.
Innumerable camping gadgets and objets - the admirable IceyTek chiller, the importance of using a self-inflating foam mattress rather than an air-filled inflatable one, a Camping Gaz stove that comes inside its own huge saucepan, Delta Pegs, the superiority and warmth/coolness of cotton canvas over nylon. 