I just got back from a trip to Shanghai and Hong Kong. We arrived in Hong Kong on the Wednesday afternoon, and went to the park that evening, then we had the next two full days and nights in the park. Prior to this trip, I would have said (and did say on a couple of 'how many days' threads) that two days should be plenty. However, I left feeling like I definitely needed more time - I certainly didn't get to every ride, and didn't even set foot in Adventureland!
Having said that, there were a few events on at the time of our visit which ate up a bit of time. First, the Thursday was the first day of their springtime season. They have character Easter Eggs to 'hunt' all around the park, and special garden displays etc. There are also all the characters in their springtime outfits, which are very popular for meet and greets. We spent our first hour on the Friday morning lining up for Minnie and Mickey, and we went straight there at rope drop. They also have a special springtime parade which is very cute and worth catching. We saw it twice.
The other event which took up a bit of time for me was the special pin trading event. This was on from the Thursday too, and I spent about an hour on Thursday morning lining up to buy some of the event exclusive pins and just generally check it out. In the end I was happy to get the special pins, but the event itself wasn't really for me. For someone who was into it though, it could have quite easily taken up a good chunk of a day. I did do some pin trading with CMs over the course of our stay, but that didn't really chew up a lot of extra time.
We also seemed to be there over grad time. We saw a few groups of little kids (like pre-schoolers) in graduation gowns and caps, and a couple of older teens/young adults in their graduation gowns/caps. I did also see some graduation pins. It didn't really affect things too much, but we did notice quite a dramatic increase in crowds later in the afternoon and into the evening.
The shows and parades in HK are well worth seeing. The shows are popular, and especially for Mickey and the Wondrous Book, you need to line up at least 45 minutes before the show time. They were cutting the line off at about the 40 minute mark as it had already reached capacity. We got in line about an hour prior to the show and were one of the first in after the VIPs. For our visit, there were 2 day time parades (Flights of Fantasy and the Springtime Processional), and a night time parade (Paint the Night). To get the spot that we wanted for Paint the Night, we started staking out our spot about 30 minutes ahead of the parade. From there we went straight to our fireworks viewing position.
If you're into characters, there is a reasonable selection in HK, and they do seem to have them in special outfits a lot. The longest waits were definitely Mickey and Minnie, followed by Duffy and Gelatoni. However, the other lines weren't short. Meeting a few characters will take up a reasonable chunk of your day, especially if you have specific ones in mind. Mostly I found that you could only meet one character at a time (ie by the time you met the first one, all the other lines were already cut off), so you need to come back to the others at their next meeting time. I had grand plans to meet loads of characters, but with everything else going on, it was too hard to work around the meeting times and I only met a handful in the end.
We also spent a fair amount of time shopping. Merchandise in HKDL has really improved over the years. They now have plenty of cute and unique items, and there is a different selection in each store. A lot of stores also have discount tables which are worth rummaging through. As there is no extra shopping and dining area, you are really limited to doing your shopping during park hours (having said that, the hotel stores do also have a very decent selection of merchandise and are open until late).
As far as rides go, they are generally easy to slot in amid the shows and characters times. Most rides are a walk on until lunch time, and again after dark. We walked on to Mystic Manor, Grizzly Mountain and Space Mountain a few times each. The longest wait times are usually for Winnie the Pooh, Dumbo, and now Iron Man of course. You may find these get to half an hour or more during busy times (which is a long wait at HKDL).
Hope that helps! Feel free to ask anything else specific that you want.