I find the reCaptha digits hard to read! Also, I think the math question is the ultimate, its easy for a human and IMPOSSIBLE for a bot to figure out. A bot has no idea that 1+7= 8

Well I think that most reCaptcha images are pretty easy to read! (but they also have sound, and you can ask for a new challenge if that one is impossible for you)

Also, computers make trillions of calculations per second... why calculate 1+7 should be difficult for some bot? According to http://recaptcha.net/security.html "others, such as MAPTCHA, consist of asking text-based arithmetic questions like "what is 1+1". These can be trivially broken by an attacker." If they are not broken right now (probably they are!) they can bypass it pretty easily in the future.

reCAPTCHA I suggest to be just one more option that the administrator can use if it starts getting fake registrations, or spam messages.