How long can I leave an open bottle of white in the fridge?
A lot will depend on how critical you are with regards to what you consider "spoiled." I have to admit that whites (or reds for that matter), do not spend too much time in the 'fridge in my home. That said, I will always grab a Vac-u-vine and give it a few pumps. I have not done a real controlled experiment, but the wines are still very good the next day, and the next. With Stelvin closures, I do not attempt to evacuate the air, but just cap, screw and place in the 'fridge - good the next day.
My "gut reaction" is that you are good for about 2-3 days with some sort of evacuation system. Again, your mileage may vary, depending on how critical you are of the wine in question. If I had a Le Montrachet, I would not expect it to be 100% the next day. I would also plan on consuming it on the day/night that it was opened, plus, I would also likely "caraffe" the wine, before serving.
One day, when I have nothing else to do, I will do a control test of several different systems for wine storage: nitrogen, argon, Vac-u-vin, nothing, plus a fresh btl. of the same wine, and see if I can detect the difference. I have several systems on-hand, but always go to the Vac-u-vin - maybe out of laziness and it seems to work well for me for short-term storage.