Last week or so I have been working with the Leight Weight UI Toolkit for Java ME. We started with drawing everything by hand using Java ME LCDUI and Canvas class, but we feel that this is not viable in the long run. We want a toolkit that gives us a higher level API and handles differences between different devices.
Impressions so far are good. It was some work converting our application for Lcdui to Lwuit, but less than expected. Performance is OK, our main problem is network traffic, which has nothing to do with Lwuit, but the toolkit does not seem to slow it down, possible even speeding things up a little (since our old interface repainted the whole screen a bit too often). We haven't really used much of the visual goodies of the toolkit yet, and that is not our main reason for using lwuit, but surely we will use them eventually.
Lwuit is inspired by Swing. In my opinion they follow Swing a bit too close. I don't really see the need for Layout Managers on these very small devices. Our layout in our main screen is position based and needs a scrollable canvas, which lwuit gives us. So far we use the (undocumented) CoordinateLayout, which seems to work as expected, possibly we will have to implement our own, but since we don't want the LayoutManager to ever move the objects and set the X and Y coordinates ourselves, it shouldn't be too difficult.
Handy features, like drawing a text centered or making a dotted line, that exist in Lcdui are not available in Lwuit for compatibility with Swing. We used both these features in our interface, so we had to modify Lwuit so that we can use them, which was not difficult. We don't really see that compatibility with Swing is important, since the interface is designed for mobile devices with small screens and limited keyboards and possibly touch screen.