I see from my forum search that there are requests for several different captchas.
Notwithstanding, I encourage the team to look at incorporating SI Captcha ( http://wordpress.org/extend/plugins/si-captcha-for-wordpress/ )
as it is free , widely used -- over 1 million downloads -- and incorporates itself with WP and other important plugins like S2Member. ( http://wordpress.org/extend/plugins/s2member/ )
The WP integration is helpful so that webdevs do not have to deploy two (or more) captcha solutions, one for GF and one for the Login screen. Really Simple Captcha is only available to GF and cannot be used directly for login or other components. Recaptcha is hopelessly difficult for many users, particularly elders.
Likewise with S2 Member providing SI Captcha integration, it is useful for GF to share development paths when possible with like-minded projects. S2 Member is the highest standard membership plugin, even in its free GPL version. (The pro version simply adds additional payment gateways). I could imagine a lot of positive cross-contamination if the two development teams engaged each other as you code for many similar or identical solutions -- maybe even including on the pure forms side <laugh>
Anyway, Please considered including SI Captcha integration.