Thanks Euro2014! Very helpful. I don't hold I-797 yet but it's good to know that once I get it "I'm safe"Frankly, I would not expect any issue for your I-485 case either way: as you seem to be holding a receipt confirmation with I-797 Priority Date while on valid J status (are you?), either you will remain in J status until AoS application has been approved, or you would attain 'adjustment pending' status if your J status, for whatever reason, should expire. Either way you will be able to complete I-485 processing. The only downside to the second scenario would be that you don't have a valid status to fall back on in case your I-485 application should be declined, in which case you would have to leave for your home country in due course. Also, in case your J Program would come to an end, you would require a DV based EAC to work in the US under 'adjustment pending' status. That's basically it, in my opinion.
The only issue I can see is if my J program got terminated before I receive acknowledgement from USCIS. I don't know exactly what would happen in this case. If you have any thoughts that would help? My gut tells me in that case I'd have to leave the US and switch to CP. I doubt this will happen (simply trying to think ahead here, just in case).