jgoodhart, the shortest that you should leave a starter in the fridge, if you want to, is just long enough to let the trub and yeast to settle on the bottom. The time it takes to do this depends on the type of yeast you use and starter size. Twice I have left a starter in the fridge for a week before, as I wasn't able to brew due to last minute work requirements. Around day 5 or so my yeast turned from a pail yellow to an off grayish color. The first time it did this I added some yeast nutrient to my wort and still pitched it. I had no issues with it; however, it did take a bit longer to kick off fermenting. The second time I did this I just pulled the starter out of the fridge, and placed some yeast nutrients into the starter. From there I placed it back on the stir plate for a day, and put it back into the fridge to see it cold crash to a healthy color. I had no issues with that fermentation at all. This is not ideal at all, but it still made excellent tasting beer.
As far as how to utilize your starter. With smaller sized starters you can pitch it all into the wort with little to no off flavors. It is best though to just pour/decant all but a couple of inches of beer off the top of the yeast cake. From there, you should allow it to come up to the proper pitching temp, so as to minimize the lag time from pitching to fermentation. I normally just put it back on to the stir plate when I start the brewing process so it is warmed up and the yeast is dissolved back into the starter for when I am ready to pitch it.