I have been running the BOINC Advanced GUI (Development Version) for Macintosh on my iBook 600 and iMac G5 1600 for 2-3 days now. The switch to this version of the client coincided with my upgrade to "Tiger" OS 10.4.0. Even though the BOINC client is not optimized (version 4.35) I have seen a clear increase in daily production on both of these machines. I don't have any firm numbers yet, but it looks like the iBook has jumped from around 45 per day to 52+ and the iBook has increased from about 140 per day to around 160 per day in credits, despite the smaller claimed credits due to an unoptimized client. Those are the results running Predictor@Home.
The BOINC advanced GUI has been very stable so far but only have about 3 days on it. I had some problems with the "Simple GUI" a menu bar control, freezing up sometimes.
Of course 3 days is not a very substantial test set, but I'll let you know how it goes after several more days. Don't know if it is the client version or 10.4, but I am very pleased with the performance improvement, especially on the iBook 600.
As mentioned on the front page, the "advanced GUI" for Macintosh feels and operates much like the GUI for Windows, including the graphics and screensaver for projects that offer it. It installs just like any other "standard" app. No terminal knowledge needed.
NEWS UPDATE: It looks like the BOINC development team has given up on trying to build a version for 10.2.x. They don't want to have to have 2 different versions (one just for Jaguar), so have chosen to support 10.3 and 10.4 more fully instead.