I don't often take an OG reading. I usually check the gravity after the partial mash, and calculate my FG with the added extracts/sugars. I generally only take an OG reading when I'm not too confident of my calculation.
When I do take an OG reading, I sanitize the hydrometer and jar, and toss the sample back in. Just treat it like anything else that comes in contact with the beer. Never had a problem. I've tasted it in the past and hate the taste of unfermented wort.
I know it is only 5 ozs, and by my calculations, only costs about 15 cents, but it just seems to be a waste to dump it.
Now when I check gravity after fermentation, I always drink the sample.