Last decade, I usually said, 'two thousand something' or 'two thousand and something' to refer to a year. Now, whenever I refer to any of the years of the last decade, I somehow got lazy, and just call it by its last two digits (i.e., 'oh-four' for 2004).

For the coming years, though, I've been calling them 'twenty-something'. I don't know, it just sounds better. I tried calling them 'two-thousand-something' or even just by their last two digits, but it didn't sound as natural for some reasons (IMO). I bet you though that by 2060s or 2070s, people will forget that we have this conversation at all, and call years in the 21st century only by their last 2 digits.