Probably quite a low percentage however it seems to be used as the proving ground for new tech such as IPv6 and ISC seem heavily into it so it's still really important regardless of market share.
Your comment above states that you'd go for Windows Server instead of NetBSD anyway... So I don't see how is this project "important".
It's the ideal foundation to build research upon which is where standards can be developed.
Everyone has benefitted from NetBSD being around and will probably continue to for a long time yet.