Here are my issues:
1) Many pages do not show a captcha, yet if I click a submit button (for example) I get a message that I must complete the (non-existant) captcha in order to continue. FAIL!
2) Other pages show the captcha box, but the box is NEVER in focus, so it is IMPOSSIBLE to click it. FAIL!
3) If I can click the box (it is in focus), often I get an INFINITE worm going in circles. FAIL!
4) If perchance I get a slate of pictures to select from, I can DELIBERATELY click the WRONG pictures and get past the captcha. FAIL!
Until Google fixes those problems, I see no reason to anger my visitors by using their captcha.