Maximum and Ideal Party Size

In light of the discussion in the comments to this post, I find myself wondering about readers' experiences with party size in their play of various RPGs over the years. In particular, I'm curious about both the maximum number of players with whom one has ever played successfully and what one considers the ideal number of players. I realize that one's ideal size might vary from game to game. A game like Dungeons & Dragons is much easier to run with a large number of characters, while one like Top Secret probably has a smaller number of ideal players. Nevertheless, I think most of us who've gamed for a long time has a general sense of what works best and I'd like to hear about it in the comments.

For myself, the largest group I've ever played with successfully consisted of ten or eleven players. This was a D&D game and the players were surprisingly well organized in their actions and ability to communicate it to me as the referee. That was the exception rather than the rule, though. Most of the successful games I've played in since have had probably half that number, which may explain why I tend to consider five to seven players to be ideal in most circumstances.

What about yourself?