It is a total crap shoot, but there are some things to keep in mind.
First, I totally agree with Disney Dreams about being kind and patient! Her instructions are excellent.
Second, it is generally harder to get a waterside table if your party is large.
Third, it is very hard to tell how long you will have to wait. It seems like they have begun giving you a very long estimated time frame, and I wonder if it is to discourage people from waiting for waterside. We've been told several times (in the past year) that the wait would be over an hour and we've only had to wait 15 minutes or less (with PS reservations). We were once told the wait would only be 20 minutes and waited an hour and a half, but it turned out they'd lost our reservation request. We were told on my birthday (party of 2) that we'd have to wait 1 1/2 hrs so we took a table in the 2nd tier, only to find that there were several waterside tables for 2 shortly after we'd been seated. We had another experience of having our reservation request disappear but we made sure to ask how much longer after we noticed a party who'd come in with the same request after us was being seated. So...pay attention to the parties around you, if possible, and take what you're told by the CMs with a grain of salt. If you've waited quite a while, ask how much longer to make sure they haven't misplaced your reservation.
Our shortest wait was when we walked in with no reservation at all and got a waterside table after about 3 minutes, but it was near the end of the time they took walk-ins for dinner. We'd noticed the night before that they took walk-ins at that time and planned it, but that was Jan. when it wasn't very busy.
Finally, we were given misinformation and, well, not told the truth on two separate occasions by a certain male CM who works in the host area. Maybe it was just circumstances beyond his control, but I will avoid him in the future! I understand that things come up, but at least tell me the truth.