*sigh* This has already been discussed to death, but whatever.
The mods are currently testing two differenct CAPTCHA systems (on all the non-PubClub members). One is the traditional hard-to-read type, the other is the ones using ads and making you copy text or answer a question. They have introduced both because of the amount of complatins from people who can't read the scrambly-letter ones. They're tallying up the number of fails from each type, and then planning to implement the most successful one.
And it's not like it's on every post - one of the mods estimated it showing up roughly once per day per user, and someone else said roughly every 20 posts. Hardly strenuous.