So I'll preface by saying I have probably not compiled SDLMAME in a year so I am slowly trying to find out what has changed since then.
I made a G5 optimized build on my PowerMac G5 2.5 / NVIDIA 6800U.
Immediately I noticed some issues navigating the UI. The keyboard is somewhat unresponsive. If I type in a game name some letters are almost always missed. I also can't seem to toggle through the different slider controls, but with the UI changes maybe I am doing something wrong. Sometimes up/down in the UI menus do not respond. This is with games that I get >300% speed no throttle. Keyboard responsiveness is horrid on games that are less than 100%. I have not noticed this issue in game having pulled off dragon punch moves in games just fine.