Tipsy, I am seriously wondering if there is something specifically wrong with your iPad 1.
I know it still isn't the most stable on that platform (the simply truth is that it has too little memory) but yours sound extraordinary.
Before he got his iPad 3, Shagpile only had the 1 (never owned a 2) so he made sure it was good on it; he had to live with it too! Jabawocky also is a heavy user of OzRunways, only has an iPad 1 and he's happy with it.
Having more Apps or music on it should not make a difference.
To answer your question: less than 10% now, and dropping fast as people flock to iPad 3s. (We saw a real spike it trials when the 3 came out and then purchases a month after; obviously people were waiting for it.)