Interesting idea, but you're gambling on a huge network effect there. I'd need to get a whole group of my friends using this for it to be worth it, and I can't be bothered to do that. Even if I could, each one of them would need to remember to update it before they went anywhere... what a hassle.<p>An idea: why not exploit an existing framework that people use for frequent updates? Add a facebook app (150m users), add twitter integration (another 800k users or so), and you're off to the races. I'd be much more easily convinced if instead of having to update your service I could just update my twitter with "eating at joe's diner tonight 6pm, hangoutable".<p>Also, do you have Google Calendar integration yet? If not, what are you doing? That's where I keep my calendar. I even have it set up to send me reminders and everything.<p>I like your hangoutable branding - there's not currently a good word for an ad-hoc social event, and you've picked a descriptive one that's also pretty catchy. Sponty is halfway between silly and awkward. Maybe you should consider rebranding?<p>Lastly, while I commend your Google account integration, I'd make it an "...or log in with your Google account" and get your own logins. Much as it pains me, the world's not ready to have all their services nestled in Google's ever-expanding bosom just yet.<p>Anyway, best of luck.