Handcent shows it, I don't think there's a way to turn off the count, only the number of sent messages.
No reason hiding it, on the flip side, why show it? Especially when you have unlimited texts. My text managers always lag like crazy, maybe calculating the thread count slows things down?
I dropped handcent and the stock app is much faster for me. When I had handcent the typing was 2 or 3 letters behind. Now, it's zippy again with the stock app.