A few months ago, the usability research team summarized some statistics they had been collecting on the subject of what people spend most of their time doing on the computer at home. Not surprisingly, surfing the Internet was number one. Number two was playing games, and in particular, I found it notable that the number one game is no longer Klondike Solitaire (known to most Windows users as just plain "Solitaire").
That title now belongs to Spider Solitaire. The top three games (Spider Solitaire, Klondike Solitaire, and Freecell) together account for more than half of all game-playing time.
Personally, I'm a Freecell player.