Sorry to be a Scrooge, but I wish people would stop doing this. It's hard enough to make a living as an illustrator in the age of digital photography and photobashing without having to compete with generic (which I mean both descriptively and—sorry—pejoratively) illustration libraries. This stuff undermines the discipline and suggests that its skills are easily acquired and the work is easily done, so there's no reason to compensate people for it.
There's a lot of talk on HN about the importance of paying for things, and while I know that most of that is in opposition to 'paying' with your privacy, which is very different from what I'm addressing here, I think the basic idea of value still applies. It's important to pay for shit sometimes. Forget the ethics of supporting your peers and just think about how it'll get you better quality, custom work.
Open-source is awesome, and I totally support anyone fighting that fight, but this kind of work is pretty clearly aimed at startups trying to penny-pinch their way into the brand signaling and associations afforded by adopting the corporate memphis look. Maybe that's an unfair read, but I can't remember the last time I saw an unfunded open-source project trying to look like every VC-backed lifestyle app that launched over the last six years.
On a particularly bad day, I can't help but feel like this kind of project is leading toward the centralization of art as a whole. It's undeniably stagnating commercial artistry.
Sincerely,
Someone who is still butthurt about Squarespace, et al. killing off small and solo web design/dev shops.