I've been toying around a bit with the TWL demos, and I noticed that they use a lot of CPU on my little subnotebook. Particularly the TextAreaDemo uses around 40% of my 1.3 ghz core 2 duo, and that for just one smallish text display area.
I did a bit of profiling with the (probably not so accurate) jvisualvm, and the results were that a lot of that time is spent in the actual openGL calls to render the text. Here's part of the snapshot from the sampler.
So I'm not entirely sure, but I believe there is room for optimization there. I had the idea of something like the option of caching text as textures or images, which seem to render significantly faster. But I haven't really looked into the code much yet, so I can't say.
In either case, it'd be really nice if drawing large amounts of text could be sped up to the point where an extensive GUI can actually run on a low-end PC, and with some pointers I'm fine making the necessary modifications myself, if viable at all.