I am using react-bootstrap but I wish I hadn't - it's quite large (113kb minified, without including anything from bootstrap itself) and doesn't do very much above and beyond using standard bootstrap classes and standard HTML tags.

It also means you'll probably end up having to include jquery for things which adds another very large amount of code...

I'm pretty happy with bootstrap as a quick good looking (with a theme) win, but I think one day I'd like to get rid of it and write some simpler problem specific CSS and use React proper for any Javascript interactions.