Responding to the OP:

You might want to close your doors when you go into your home too. I have a building that is 100% lit up. Every other block is a glowstone, in a diagonal pattern. There's no way a mob can spawn there. The outside is 100% lit up, every five blocks there is a glowstone, for about 30 units around my house (in a square-ish circle). Mobs can spawn outside the light and walk over that distance, and then get within the 10 block sight limit, and walk towards you. It's happened to me more than once (more like "more than a million plus one times."). No matter how lit up your area is, mobs act randomly when not in interaction with the player (at least as far as I know of). Meaning, they can spawn the 80 blocks away (I think that's the limit for active area around a single player?) and they'll eventually come to you within the 15-20 minutes of night (at least seems that long to me). As well, two objects moving have a higher probability of meeting each other within an enclosed area as opposed to one object at rest while the other moving. In this case, the enclosed area is the active map around you (as I believe they won't go into an unloaded chunk, as far as I can tell... meaning the 80 block distance chunks, not the chunk in front of you that hasn't rendered yet). Yes... this time I overanalyze.... but it was needed I believe. Mobs be evil, can't be too protected. Remember kids, when you get older... don't go to smokey the bear when you have problems... he only knows one line. -_-