We chose to use the Nitobi library for our Syrinx Community Server (SCS) product about 2 years ago.  We struggled badly with the ASP.NET library that came from Nitobi, but could see lots of potential for their basic javascript so we wrote our own wrappers.  When Nitobi decided to make their javascript code base open source, we did the same thing with our Nitobi control wrappers.

Nitobi isnt really a .NET dev shop, and thus they never really put a serious effort into their ASP.NET wrapper library for their javascript controls.  They are also focused on working on paying client projects which has completely taken their focus away from the javascript controls and they have done no work on the ASP.NET library.

We also have made changes to their open source javascript, but since they put our changes on a branch, the changes dont get made available to the general public.  They are supposed to review the changes and merge, but again, they are too busy with other things to deal with it.  For example, there are common javascript function names in the nitobi.grid.js and nitobi.combo.js such that if you use both controls on the same page there will be problems when the order of the js files is grid first and combo second.  We fixed that.  We've also made it possible to use the JSON libraries that inject methods in the string and other javascript classes. 

Because we use the Nitobi controls daily in our development efforts of SWAF and SCS, we know when stuff works and doesnt and we fix it (most of the time).  The management pages of SCS heavily use the Nitobi controls so we push the limits on them.  Here are some screen shots that show how we use the Grid and Combo.