Yeah we've been 9 months in development and ~6 months in private beta, got a few dozen users who've really helped shape the direction of the system and turned it into something amazing.
It's really the "what happens next" bit that I'm not sure about.
It hasn't really been "stealth", it's been "controlled", it's an analytics service (not for websites) and we wanted to be sure it worked + not get raped by traffic we couldn't afford to scale for during development.
I think your fears are unwarranted. Every entrepreneur seems to have these happy fears. Oh no, what if my site crashes under terrific load! What if super-VC Paul Schmaltz sees a bug in my website!
Even if you get enough traffic to knock down your server, that will just be a boon.
And it's better to get your software out there half-working and get feedback than to build something nice and have to rebuild it after you find out the average user wants something else.
It's really the "what happens next" bit that I'm not sure about.