Right away, let me assure you that tracks.tra.in (and the rest of the tra.in family) is in no danger, economic or otherwise, of going offline. We run high-traffic sites and are really against downtime. Since 2007 we've been using Slicehost and have been really happy about it (as were the users who emailed, thanks)! tracks.tra.in runs on a superfast 2GB slice, with a separate MySQL slice. (If you want to host Tracks for yourself and would rather administer your own server, we recommend Slicehost; please mention train@tra.in or use this link if you'd like us to earn a commission.)
This site is hosted as a micropayment-supported free service,. I've made some small tweaks to Tracks, and provide addresses for todos by email/SMS, but nothing worth a mandatory fee. Google ads won't work for tracks.tra.in, since that would mean giving Google a look at your personal data to get keywords. We hope to use Paypal's micropayment rate to scale: even if only a fraction of users buy a $0.75 microsubscription (and receive DB priority, perhaps) the site could pay to grow on demand.
I promise not to sell your data to anyone, and to respect your privacy. I do not perform data-mining or any other creepy activities on your data. These issues are very important to me: I research privacy-enhancing networks, and once administered my school's Tor server.