A question like this seems akin to starting a religious discussion; I post with a bit of trepidation. But just a bit. I'd like to hear different theories on when is the best/right time to start as a DMC.
How does one know when one is ready? I've seen it all -- naturally comfortable divers who go straight into DMC after ow/aow/rescue and are wonderful; and divers who waited years to do it and still kinda stink. =-) For me... I can't decide when to say when... here's what I'm thinking:
When I hit #50, take the UTD Essentials class which, I've been told, will mop up any bad habits I have (and I'm curious about the DIR philosophy; not so much in tech diving, but in a tech like approach to rec). Then, pick the instructor I want to DMC under (will be PADI because that's pretty much what's available here [edit: Willamette Valley]). At this point, DM is as far as I plan to go.
A little about me: I started OW in November 09 and to make along story short, I'm hooked. Only 40 some dives though. Love warm water, but like cold water, too. So much so that my husband staged an intervention after I drove to WA four straight weekends to dive in July/August. =-) (One reason I love him: he said if that's what I wanted to do, it was fine, but we did have a house and dogs to take care of so we might have to talk about how to handle the split responsibilities of a household, etc.) The experience has brought me more into my body, made me physically and mentally stronger, and rekindled a childhood dream of oceanography. The focus and meditative nature of the act, coupled with the incredible thrill of exploration, nourishes me like nothing I've ever found.
I'm not your average female diver: I'm a very large woman (but gettin' smaller every day, thanks to being brought more into my body). People seeing me do this has resulted in many great discussions about what people dream of doing, all the things they let stop them, and how to bust through those (whether we're talking diving or anything else). So I have a passion especially for helping women enter diving, and the sensitivity of what challenges large folk have with getting the right gear, etc.
As someone who thrives on connecting with people, sharing my modest knowledge of diving really excites me. I love talking to the kids at Alki or Les Davis, for instance. And the adults, too. :-) But what really solidified this thought to go to DM was assisting my sis in law. She finished her OW class w/ difficulty, and was wanting to get into the water, but not comfortable doing so. I thought long and hard about whether I was ready to assist her -- it's one thing to have your own routine down, know you can keep your sh*t together when diving with someone of equal or better skill than you (who you are confident can likewise keep their sh*t together). But to enter the water with someone who KNOWS they panic in certain situations... I thought long and hard about that before offering to work with her. I felt I was ready.
Don't get me wrong, it was a long hard day... but I loved it. Even when she was freaking out at the surface and climbing on top of me to get out of the water, I was having fun. =-) (Her lack of water comfort was primarily at the surface; her vest tilts her forward, which causes her to be uncomfortable. Her ankles start to rise behind her, she starts to move her legs which of course pushes her further forward and... a nice loop which causes an explosion of panic. It took me a moment to really accept that she did not know or no one had told her the obvious: flip onto your back when you hit the surface, and let the back inflate push you up out of the water. That one piece of advice helped her immensely.
She wanted to stand on land, drop down to the bottom (if that's possible in 3-4 feet of water) and then crawl along the bottom, dirt diving her away along, never NOT touching the ground. This behavior was allowed, I assume, to get her through to the cert. We spent about half an hour on the surface, then did a few simple drills to get her focused on something else and then did a nice easy "exploration" dive no deeper than she could CESA. It went well... unless you were behind us.
By the end of our 2nd dive (a good 45 minutes at Alki Cove 3) she was doing much better, able to swim to the buoy, drop down to 30 ft, and I got her 2 feet off the bottom by the end.
Through all this, she has a great eye for spotting critters -- she's comfortable once UNDER the water for the most part, but will need work with really getting comfortable in the 3D world of water without lying on the bottom. I had promised to hold her hand the whole time if she wanted to, and when halfway through our first dive she pulled her hand away by choice I smiled so big I almost lost my reg.
So I dunno... setting some arbitrary point like get X number of dives seems silly... and I think I'm ready but... what if I don't know what I don't know!? :-)
with water and drink it, not snort the powder directly from the packet, right? 
" - Spatman
I decided that I wanted to actually enjoy diving, and that if I wanted to help mentor newer divers I could do so just fine informally rather than follow a set path. Because I did not have the goal of becoming an instructor it didn't make sense for me to go on.
More fun, more seeing the pretty fishies. Part of me probably already knew that, because otherwise I would have DONE it instead of pondering so much if I should do it. 
