I will be going through the PVG again next week and the week after for my trip.

First will be AA LAX - MU PVG - BKK and then return KA HKG - AA PVG - ORD. I'll let you know how it goes, but I've never been able to check through the bags to/from the US. Only from Japan to HK via PVG.

One agent told me a few years ago that the US has stricter regulations so the bags need to be scanned at PVG that's why you cannot check-through there, but that might not be true if they allow it from PEK.

Regarding transit tmes, PVG is often delayed. I have 2hr 40 mins between the HKG - PVG - ORD flight. That's enough time if there's no delay, I hope that's not a prob.

Lastly, I heard others talking about the AA transit desk, but with the need to recheck the bags, is there any point to get the boarding pass there as opposed to the normal desk outside?

I doubt that the baggage check restriction is from US regulations. I've checked bags to and from the US with multiple transit points on both ends with little problem in the past. PVG is the only transit point where an agent told me flat out it wasn't possible due to local regulation.

Looking at historical times for AA182, delays of 30min+ aren't uncommon. Hopefully delays of >2hr are rare, but with any overseas flight with a single aircraft turn, it's not out of the question.

If you need to recheck bags, I don't see any need to collect boarding passes separately. It's not (like the US) where you can drop bags after customs without a formal recheck - you must recheck with an agent anew.

However, if you had no checked bags - I presume immigration/customs clearance isn't necessary, provided that there is a transit desk and transit security? Can anyone confirm this, or do all/most transits require immigration and customs clearance?

Transiting in PRC airports will require going through immigration, there are separate lines for transit passengers in PEK, not sure about PVG. No need to recheck bags in PEK, but apparently it is needed in PVG.

I guess most of the people above have answered the OP's question.

Actually AA has advised me the same thing. Here was my experience:

I flied from Sydney to Houston last December. Initially I planned to fly CX to HK then PVG, then AA from PVG to Chicago then Houston... lucky I called AA and they have advised me I have to recheck everything at PVG if I wanna go that way...

I end up with CX from Sydney to HK, then Narita, then Dallas then Houston... luggage went through all the way to Dallas (need to recheck there) from Sydney.

Just back from my trip, did not interline bags, had to pickup and re-check in PVG, but actually PVG has gotten much better recently, atleast terminal 2. Immigration lines are long at times, but often they will open more windows and bags are out before or about the same time i make it through immigration.

For transit you need to make sure you have a printed itinerary with your passenger name on it. (They asked me both times where my name was.)

Just a tip, if you need to store bags, you can do so at either end of the departure upstairs level, just take the elevator up once you enter the arrival halls, many elevators to choose from.

AA LAX - MU PVG - BKK and then return KA HKG - AA PVG - ORD

I would allow about 3 hours to be safe, but should be ok with 2 hours as long as your flight isn't delayed, which is an issue w PVG.

talking about which, some CX F checkin agent also told me the same nonsense for HKG-LHR-EU overnight transits. the BA agents told me that is not true so i had to haul all my junk in london....
if you're interested, i had to go into london and arrive at 2100 and leave at 0730. i hadnt had time to go to T5 and put them in storage. and they cannot checkin the day before - but interlining for TRANSITS are ok.

LHR has always been crystal clear - any transits less than 24h from scheduled touch down to scheduled take off means your bags can be tagged through. I've done an EK/BA/AA combo - MAA-DXB-LHR-DFW and had no issues having my bags tagged all the way.
Also done a BA/9W - NYC-ba - LHR 9w-BOM-MAA and had them again done all the way. Both where with overnight layovers at LHR (late morning arrival, next day early AM departure). This is regardless of terminal / airlines. So if you are taking CX 253 in and then flying to EU next day on BA, they really shouldn't be making a fuss.