I checked out libRocket in the past but it always looked inactive to me. The last news on their web page is from 2011 and the forum is not exactly active but not completely dead either. Do you have any more experience with that project? Are they still actively developing?
I started using libRocket, with SFML/OpenGL rendering, two weeks ago, and I like a lot of the features and available controls. It's also fairly easy to add custom controls and expand existing controls.
The initial learning curve was a bit steep, it's a bit incomplete in places (ie I had to add a row selection indicator to the data grid), and similar to using HTML & CSS, it takes some trial and error to get things laid out correctly.
Data and event binding are really easy to setup, and it's easy to customize the look of the data. The code is well organized, so it's easy enough to add additional functionality. And, once you understand the paradigm, it's fairly easy to layout a dialog or UI.
I've only ran into one significant snag, and that was trying to use two data grids in a single window. I could easily use a data grid and a data selection element. I could have done something wrong, or there might be some formatting requirements that I didn't understand. I ended up not really needing it, so I didn't spend much time trying to figure it out.
I looked at a lot of the GUI libraries available, and can't find one with an advanced data grid control. Many have a list control, but very few have a data grid control, and only libRocket had support for data binding.