I'm one of the developers working on Mantano Reader. We are taking all of your comments into account, thanks for your suggestions.
Concerning the speed issue, could you elaborate a bit on which parts of the application feels to slow ? We are testing on different devices (2.2 and 2.3 smartphones, Archos tablets, and Honeycomb tablets) and the overall speed seems good when compared to most of the other reader apps.
The text selection with handles and the word highlighting in PDF files is on our todo list. The back button behaviour is currently being fixed.
We also checked ColorDict, and are considering its integration into our reader.
We hope we'll manage to convince you to buy the application someday ;-)