I am using Flash, and happily haven't seen a WoWAce/Curse CAPTCHA since the bug with Opera/Windows was fixed. I was speaking more generally though, about the problems with the small sizes of CAPTCHA images... it's like the first CAPTCHA implementation was designed for 640x480 resolution, and ever since then everyone else has just stuck with those image dimensions... :p
I understand you on the size of Captchas as some of the ones I have to deal with to enter some sites have been ridiculously hard to see. I wear glasses, however my corrected vision is close to normal. Yet some Captcha's are an complete pain in the ass to figure out. Is that just a sqiggle or is supposed to be a letter? At least reCaptcha is generally readable although that does depend on the original scanned source's condition.
The other thing to remember about reCaptcha is those words that you see in the Captcha are acutally images of text from the New York Times archives and the Internet Archive. So that 1/4 or 1/2 was a printed image that has been digitized.
I frankly never have had any issues with Flash and Firefox (and I have NoScript installed). However some people have this "Flash= Bad" attitude likely stemming from sites that use Flash way too much or poorly coded Flash apps.