Although the recently released version 4.0 is still in beta stage but when considering it's features and user feedback it has received so for for the beta version, it's sees as good as any released app.
Thumb Keyboard fully support Android Gingerbread (2.3) and higher, including the separate honeycomb version which is aimed at tablet PCs as well.
*. Easily switch between various keyboard layouts.
*. Multi-touch gesture support.
*. Better shortcut support - Say that you have frequent words/symbols, etc then you can set-up a shortcut for speeding the process while typing.
*. Resize keyboard buttons easily. If you have somewhat big fingers and found out that even though your screen still has a bit of a room but still the default keyboard app won't let you change the size, etc... but with TK4.0, changing a button size (both height/width, etc) is a breeze!.
*. With this new version, you can easily access the frequently used keys too.
*. Better predicting algorithms - Meaning that, while you type the app will be able to "guess" your words, again resulting a faster typing speeds.
These are just a few of its main features to mention. Anyhow, if you want to give it a try then please get it from here. One more thing, if you're using the current market version of Thumb Keyboard, then please make sure to uninstall it first.
As mentioned there could still be bugs, so be aware of it. While I was reading this official release thread on XDA forum, for few "bugs" that were reported, the developer suggested that after installing, if you reboot your Android device, those "bugs" would be automatically resolved. Good luck.