I am in the same situation. I have three players, all good friends. One recently became a new father and attends about half of our sessions. We play on Thursday nights from 7-11.
With my players, I find that I rarely have to adjust the adventure as written. We mostly use Dungeon adventures with some slight modifications to make them fit our campaign plot. With only three PCs, sometimes we miss a certain character type (we don't have a cleric or rogue for instance). If I see that a missing character type is going to be needed for an adventure, I'll script in an NPC to join the party on a temporary basis.
For campaigns with only three PCs, keep in mind that they will advance much more rapidly since they are dividing XP three ways instead of four. They will get more treasure for the same reason. Think about decreasing the number of encounters in a published adventure.
You'll have to think about what to do with your 0.5 player, too. ENWorld usually has a bunch of threads about what to do with occasional players. My philosophy is: we are doing this for fun. I'm not going to punish a player because gaming isn't his first priority in life. So when a player can't make it, we try to come up with a plot device to explain that PC's absense. If there is no good way to explain it, we have another player control the PC. If that missing player's character is so central to the night's session, we wave off and play an alternate game.
Its actually pretty fun to have only 2-3 players. Each PC gets more spotlight time and is more important to the overall plot. And you don't go through as much pizza and beer.