I've always had this in memory but never use it for anything useful, however I thought I'd share with the world rather than keep it to myself. The impact is that a spammer can enumerate what should be hidden e-mail addresses with the aid of CAPTCHA cracking services such as deCAPTCHA.
You can use this query, or scan the web yourself looking for these URLs. The best way would be to create your own e-mail hiding script, one that is unique, that way spam bots won't have a clue what they're doing.
Spamming users of recaptcha would be a waste of energy they are very unlikely to succumb to offers of cheap Viagra. However social engineering attacks would still be viable.