I've recently discovered a profound secret concerning fanfic-writing that I feel compelled to share: Readers, for the most part, couldn't care less whether or not you use a beta, and, in fact, would prefer you offer speedy updates over flawless writing.
How did I come to this conclusion? Experience. During my time in the Twilight fandom I believed whole-heartedly in the do-not-post-until-this-has-been-beta'ed-and-pre-read mentality, believing that readers cared as much about quality and professional-looking writing as I do.
However, my recent experiences in the Harry Potter fandom have taught me otherwise: I posted all 25 chapters of Hallowed Hearts in little over a month, unbeta'ed, and received numerous compliments about my super-speedy updates.
On the flip side, while writing my first novel-length fic, In Pursuit of Normalcy, I never once (that I can recall) received a review along the lines of, "Thanks for taking the time to assure that this is beta'ed and relatively error-free! I appreciate professional-looking quality!"
Instead I got several very rude complaints about the wait between updates when my beta was dealing with a personal crisis, my stepmother had died of brain cancer, and my daughter was hospitalized. Did I explain any of this to my readers in detail? No, because I didn't think it was any of their business. I assumed that it was assumed that I would update when I could, that laboring for free was hardly my top priority. (By the way, my chapters were all between 6 & 12K words and I never took longer than 4 weeks to update, & I unfortunately allowed that fic to consume WAY more of my personal time than I should have.)
All this has led me to the conclusion that as long as I'm writing as an amateur, I'll never go back to using a beta. Not having to wait for a chapter to come back from a beta--especially now while knowing that readers don't appreciate it anyway--is rather freeing.
Now do I think that EVERYONE should opt out of using one? Not at all. Some people are in dire need of one; but at the same time, I've seen "beta'd" fics where the beta evidently had no clue what they were doing. (For instance, I'm currently reading a fic where neither the author nor the beta apparently know how to punctuate quotations, even though I gave the author a specific example in a review.)
I'm not saying that my writing is perfect or error-free (not even my beta'd fics), but I AM saying that it's error-free enough for the average reader, who isn't, for the most part, particularly critical. (If you don't believe me, you should see the reviews left on the above-mentioned fic: Apparently no one else is bothered by the fact that Ron was written off as a moronic ogre, or else they don't think it worth mentioning.)
And...that's my rant of the day. (Lame conclusion, I know.)