I'm not the oldest Play by Poster by far, but I've been around here since well before the forums became as large as they are now. I mean, were not rules or GD, but were next in line now. At one time, we had maybe 12 active threads, and that was including the Industrial Revolution Game. I must say that although everyone says that combat bogs down a game, I've seen it fly by as well. Fly-by combat, though, requires players to basically be online at the same time as the DM. Games with more than 4 people really limit that possibility. Sometimes 2 seperate characters (me and Sollir in one case) can finish thier combat rounds at an incredible pace compared to all 6 of us. I have leveled up a few times, but only in the Psionicle. I've had PCs level up before, but only in the Light Hearted Hack N' Slash adventure. They were going to be hitting level 6 (after starting at first), but this was because when the game was active, it WAS a LHHS.
Currently I only DM 2 adventures, and play in the Psionicle, Emerald's Game, and have a character in LEW, but other than that I'm a bit too busy. I have an adventure I'm in that is ran by Kalanyr, but he hasn't been updating. My major boards occupation nowadays is play by post moderator/Living EN World Judge.
I have never played in an adventure that has finished completely, nor have I ever DM'd an adventure that completely ended. This is mostly because none of the games I run or play in are supposed to end. Emerald's PbP "ended" but we all opted to continue this as a campaign.
My most fulfilling experiences so-far have been the LHHS and IR. The IRR was the most work intensive DMing project I ever undertook, but LEW is catching up quickly.
One thing that's just LEW related is that the players are really anxious, and I'm just not sure about a lot of things. I'm not one to rush stuff, especially things like class proposals and abilities.