Let your users create the site for you. Iterate and evolve. Start with something that works, get people in it, and build it together. Have a slow beta. Invite new people on slowly. Talk to the users about what they want every single day. Let your users help build your site. The result will be more reassuring, comforting, intuitive, and effective.
Let your users fund you. Ravelry was funded in part from users who donated $71K. That's a gift. Not stock. Don't give up equity in your company. It took 6 months of working full time and bandwidth/server costs before they started making a profit and this money helped bridge that gap. They key is having a product users feel passionate about and being the kind of people users feel good about supporting. That requires love and authenticity.
Become the farmer's market of your niche. Find an under serviced niche. Be anti-mass market. You don't always have to create something for the millions. The millions will likely yawn. Create something and do a good job for a smaller passionate group and that passion will transfer over to you.
Success is not about scale, it’s about sustainable execution. This lovely quote is from Jeff Putz.
The database is the problem. Nearly all of the scaling/tuning/performance related work is database related. For example, MySQL schema changes on large tables are painful if you don’t want any downtime. One of the arguments for schemaless databases.
Keep it fun. Casey switched to Ruby on Rails because he was looking to make programming fun again. That reenchantment helped make the site possible.
Invent new things that delight your users. Go for magic. Users like that. This is one of Costco's principles too. This link, for example, describes some very innovative approaches to forum management.
Ruby rocks. It's a fun language and allowed them to develop quickly and release the site twice a day during beta.
Capture more profit using low margin services. Ravelry has their own merchandise store, wholesale accounts, printers, and fulfillment company. This allows them to keep all their costs lower so their profits aren't going third party services like CafePress.
You can do a lot with a little in today's ecosystem. It doesn't take many people or much money anymore to build a complex site like Ravelry. Take a look at all the different programs Ravelry uses to build there site and how few people are needed to run the site.
This story is not bad the RoR site with daily 3.6M pageviews. However, I'm wondering how it compares to the similar site running plain old PHP.