cgregory
Now that I have gotten the legally required Canadian greeting out of the way, I can get around to introducing myself.
I've been using OP for about 2 months as a player in the Shadowrun campaign "Geek The Mage First":http://www.obsidianportal.com/campaigns/geek-the-mage-first playing the Mage of the party. Obviously, a good choice considering the title of the campaign. I've argued that since Sam Wolfe is a shaman rather than a mage he should't be geeked first, the men with guns typically haven't thought that argument carried merit. :)
I've definitely found that OP allows for some great player input in the running of a campaign by allowing players to easily add to the story. I'm always finding it interesting how different players at the same table can see very different storyline progressions. Of course this is even better when all this is being done from the character's point of view. In my opinion I think this is one of the best things OP does to improve any game, it helps the player/GM communication about the storyline at least from a player's perspective. I haven't used it as a GM yet, so my experience with OP in that way is limited, but the GM secrets seem to be useful for doing prep beforehand.
During a game I can see OP as being useful as an online reference to old NPCs and such. Does any one use it as more than that during a game? What are people's favorite applications for gaming? Personally, I love using RPGTool's Maptools and displaying it on the plasma TV and player's laptops for character movement. This is especially true with large or numerous maps.
They are among us!

XCom: Defiance - Campaign of the Month November 2016
Comments
Let everyone in your group know that's a darn fine wiki you've put together, as in Featured Campaign-worthy.
I'm using OP to run "our _Flashing Blades_ campaign":http://www.obsidianportal.com/campaigns/le-ballet-de-l-acier ; it's the first time I've run a game using a laptop to store pretty much everything, and I've gotta say it's invaluable for running a 'sandbox'-y setting with lots of places and character relationships to track.
In addition to Obsidian Portal, I use a "Flash-based version":http://artifex0.50webs.com/GMEmulator.swf of the "_Mythic Game Master Emulator_":http://www.mythic.wordpr.com/page14/page9/page9.html to "increase stochasticity":http://forum.rpg.net/showthread.php?574031-Using-Mythic-Game-Master-Emulator-as-a-refereeing-tool-two-actual-play-examples in the game.
Looking forward to reading through your adventure logs.
Mike aka Black Vulmea
"_Le Ballet de l'Acier_":http://www.obsidianportal.com/campaigns/le-ballet-de-l-acier - swashbuckling adventure in the age of the Three Musketeers and Captain Alatriste
I also agree that OP looks very nice when displayed on a plasma screen as a visual aide accompanying a session. Like Black_Vulmea above said, it's truly invaluable.
Mike your flashing blades campaign is extremely detailed. How long have you been putting that together?
Dyluth, I'm guessing that either you or one of you players if a fan of OOTS based on your Star Wars campaign graphics.
They are among us!
XCom: Defiance - Campaign of the Month November 2016
I started working on it when I signed up for Obsidian Portal two years ago, but at the time I was in the midst of a career change and I didn't actually have time to run a game, so I kinda just picked at it here and there. Once I started looking for players last summer, I knuckled down quite a bit more.
Thank you for pointing out the detail - I tend to see only the many, many holes yet to be filled.
Mike aka Black Vulmea
"_Le Ballet de l'Acier_":http://www.obsidianportal.com/campaigns/le-ballet-de-l-acier - swashbuckling adventure in the age of the Three Musketeers and Captain Alatriste
Unfortunately where our group plays there is no wifi so I have to use stuff printed off, which I keep in two black books. However, I have written the whole campaign on OP and it is a brilliant resource when I am doing revision and preparing for the next game. I tend to make short notes and a few helpful tables in Excel to take to the table.
twiggyleaf
"I met a traveller from an antique land....."
CotM May 2016: Mysteria: set in Wolfgang Baur’s MIDGARD.
Previous CotM Aug 2012: Shimring: High Level Multiplanar Campaign
Inner Council Member
As to your question, as a world builder and a DM, I did make substantial use of my wikis in-game, since there was just too much information for me to keep track of without it. For instance, when the party is about to embark upon a journey, we'll pull up the maps to gauge distance between locations. When I reintroduce an NPC from the past, I first quickly glance over their bio. When questions crop up about the law or politics of a specific region, I consult the locations section. All in all I'd say the Portal has been the single greatest innovation to the way I DM that I've experienced.
Cheers,
-Arsheesh