The productized version is just that -- productized. Specifically, you can get Sun support for SJAS 9.1, but not for Glassfish.
There may be some other differences between the two, I do not know if Sun is bundling any binary only bits for 9.1.
SJAS 9.1 MAY be more thoroughly tested than Glassfish, or may be tested differently.
Glassfish will soon have a UR1 patch update to handle issues that couldn't be resolved by release time, but SJAS may not get those changes until a little bit later as they go through their internal processes.
So, unless Sun is bundling any extras that they can't release with Glassfish under Open Source, the primary practical difference between the two is that you can purchase support from Sun for SJAS, but not for Glassfish.
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