I wouldn't say 'high performance VM's' but rather cheap prices.

I recognized their name from Packer.io, for which there is a DigitalOcean-specific builder: http://www.packer.io/docs/builders/digitalocean.html.

Given that it's a fairly new project and DigitalOcean is a relatively unknown cloud (relative to EC2 the other cloud-based builder in Packer.io), I wondered if they had also perhaps contributed heavily to the project. That's another good way to see a sharp rise in popularity from developers!

Are their VM's performance on the same level as the others you listed or higher? What do you base the "high performance" comment on?

They differentiate themselves by offering SSDs for all instance sizes + offering a very cheap level ($5). While SSDs won't improve all workloads, I think "high performance" claims compared to the typically IO-weak alternative isn't unreasonable.

Also, they're popular enough now that I'm surprised people haven't heard about them (especially after recent funding)...

Yes, at least. For one I believe all DigitalOcean boxes have SSDs. I've found their boxes much better per $ than an EC2 VM. EC2 has a much wider tool suite and is possibly better if you regularly spin machines up and down. YMMV, but for just 'a box' they compete pretty well IMHO.