Content marketing into emailed drip campaigns and/or retargetting is a pretty powerful formula in many SaaS businesses. Scalable content creation can be a pretty powerful force multiplier at lots of businesses, including SaaS businesses.
A service which is remarkable enough to mention to friends, or which intrinsically gets mentioned to other people in the course of typical use (e.g. Basecamp), is a nice asset to have, too, but many SaaS companies grow without those advantages.
Anyway, I guess, retargeting is something powerful if you are able to bring a user on your site at least one time.
Are you suggesting that their growth is caused by "only" content marketing + retargeting + remarkable product?
Do love digitalocean though.
1) Identify several use cases and features for your application (preferably more than 10). Examples for a project management SaaS app:
- Project Management
- Time Tracking
- Increase Productivity
- Team Collaboration Tools
2) Build a keywords list, you want to get 3 to 5 keywords for every use case.
3) Create landing pages targeting every use case and feature. Use the keywords you previously identified in the page title. You should have good and useful content on these pages and it should focus on converting visitors into customers.
4) Build inbound links for your homepage and every landing page. Analyze backlinks of your competitors and related products using http://www.ranksignals.com (disclosure: I built RankSignals). This should get you an idea of how to get links and how many links you need.
5) Reach out to as many blogs as possible and pitch your product. Don't just focus on most popular tech blogs, every single link helps; even a local mom blog.
With in few days or weeks (depending upon your competition and execution), you could start ranking on search engines for most of the keywords you are targeting, and it will start driving a growing stream of organic SEO traffic to your product. Industry influencers and bloggers will also start noticing your product and write about it. This will drive even more traffic and links.
This will build an organic marketing flywheel which will bring new customers and continue to grow every single month. You can scale this by creating more landing pages and useful content like guides and tutorials. DigitalOcean does this very well, their community content portal (https://www.digitalocean.com/community/) drives majority of their organic traffic.