What is it? That isn't clear to me at first or even second glance. It's nice that you provide information such as "do I need to make a long term commitment?" but first make it clear a commitment to WHAT?
Edit: I see, you linked to the signup page. Perhaps not the smartest thing to do.
I stared at your frontpage for a good 3 minutes (great design, by the way), and I still have no idea what it is that you are offering. What exactly is "Flowdock"?
You really need to work on your website content. The design is very nice, but after TRYING to figure out what it does (which most people wont do) I really don't have a clue. Your about page is a bunch of marketing speak which doesn't mean anything and the home page isn't much better. What can you do for me and what is my problem that you are trying to solve? The tour gets close, so move much of that to the home page and try again. I really like how the site looks but I don't know what it does... sorry.
I think this is an awesome implementation of what can be a tricky concept.
Out of curiosity, what percentage of users use their Google accounts? Facebook accounts? Have you noticed any trends in terms of "serious" users (e.g. higher plans, more likely to convert to paid users) using a Flowdock account vs. their Facebook or Google?
I've always thought that Facebook/Google sign in worked well for free sites or "lightweight" sites (e.g. ones my entire business doesn't depend upon), but I'm curious how many people use them effectively with a site like this that's more "vital".
We rolled out the FB/Google signup/login today, so we don't have any numbers about the usage yet. We'll need to do a blog post about that when we have some hard data.
Are you showing us the sign up form or the application (flowdock.com)? I don't understand what FlowDock.com is (tho I do know that you have a 30 day free trial).
Edit: I see, you linked to the signup page. Perhaps not the smartest thing to do.