If you need a Grid or TreeGrid that can efficiently handle thousands of rows, this might work for you. The LazyLoad grids work similarly to the LiveGridView, except that the Store will always cache results and the View will only ever render the rows which are visible. For me, this has translated into significantly better response from the UI.
This has not been extensively tested and has only been tested with FF 3.6 and Chrome, so you might need to tweak it to get some aspects to work for you.
Attached is the LoadLoad module, and a sample app that shows how you use it.
Ideally, the GXT developers would find this useful and integrate it. This should be a fairly simple task, and the code could be significantly cleaned up with some minor refactors.