I did flash my i9300 with MIUI ROM...
I did get a GPS lock in Siygic in under 5 seconds, so I guess it works here. I did the steps that user Reino mention a few posts before this one, so I guess it helps, thank you.
I do experience some graphical issues, but they are occasional and understandable since it's a 720p phone unlike most MIUI phones.
As an android app developer, I will see the internal errors when I will plug in my phone to the computer, but that will happen next week, I try to stay away from programming during the weekends
ONE THING I HATE ABOUT THIS ROM:
Every time I download an app from the market using mobile network, I get that dialog telling me not to download because operator could charge me for downloaded data. Sure, it's good if you have a limited data, as for me, I don't! Make a ******* checkbox in the settings to disable this messages, cause I don't care about the data transfer.
P.S. the default data size of an app to even display this message should be about 30MB and not 1MB