I moved minecraft.novylen.net to a RAM disk yesterday. Performance issues have been resolved entirely. In a stress-test today, I had 30 users logged in without a hiccup. It’s pretty easy to see how a server with more memory and better CPU could support 60-100 users.
Currently I am limited only by bandwidth: the package we have right now is $150/mo for 130KiB/sec upload, but latency issues when the upload is as little as 75% saturated (sigh, as much as 3 seconds ping time to fraser.sfu.ca) mean that the ISP has temporarily put us on the $300/mo package with 750KiB/sec upload, which is nice. With 30 users, the server did a pretty steady 300KiB/sec up. So we could easily support more users if I could find a way to partially fund it.
Subscriptions will help, if I can find the right combination of carrot, stick, and price. It doesn’t seem to be the price so much as the concept of paying a subscription, or donating, that people have trouble with. So I’m aiming for $2/mo, which is pretty comparable to iphone apps. I only support paypal at the moment.