I've been using GalnetMiui for a few months ever since the early beta days up until one of their most recent Chameleon RC2 release before switching over to MiuiAndroid. My understanding is that Galnet's team tries to improve the official Miui rom with features and functions of their own, but since Miui is a closed source they were restricted. They have recently implemented their own framework which is great but with it comes teething problems and stability issues.
I've grown tired of flashing their new release only to re-flash back to an earlier (more stable) version. Great effort on their behalf but for someone who is just after a stable, clean rom with good battery life on all future updates I think official Miui is the best way to go. This is why I have switched from Galnet to MiuiAndroid rom.
Bloated in a way that they still have the compass, the 3D gallery and an extra off app here and there. But i find the battery to last longer on my galaxy s. I know there are a lot of under the hood optimization for the i9000 but nothing major as far as user experience goes.
His last v4 build had a monstrous battery life and an extremely fluid UI
I have to say that battery life is noticeable longer on Galnet 2.2.10 than it ever was on the Official MIUI versions I've run. Whatever they've done Galnet does not ceaselessly fun "Android System" processes that violate your battery all day long. I generally have 60% and up charge left on my extended battery after a full day of use. I have not had to do battery pulls like I did on Official, though those were not nearly so common as they were on stock Froyo or GB so I can't complain.
Galnet is great and I'm glad the devs took the time to port it.