The sound should be perfect on GG and good on most GBC titles. When the emulation is not keeping up (some GBC titles) you will hear breakup of the audio. Try setting the frameskip checkbox or turn off audio if it is really bad.
The code is all written in C and does pretty well on GBC, but when GBC titles enable high speed mode (8Mhz Z80), the 132Mhz OMAP has a hard time keeping up. GBC should run all titles full speed on a decent 200Mhz device. A good GBC game to test is "Galaga: Destination Earth". This game taxes even fast smartphones. Anyone with a 200Mhz smartphone, please let me know if tough GBC titles run at full speed.
If all goes well, I should be able to release it by the end of the month. Obviously not everything will be perfect, but I hope to have reasonably frequent updates.
I'd really like to hear suggestions about the UI and feature set. E.g. how to enhance the save/load state and friendlier ways of defining the keys, etc.