Elmah is one of my favorites, works very well! Setting up Elmah wasn't that hard, but is made much easier now through NuPack support!
Yes, First I downloaded the Source for Orchard and after doing a build in VS 2010 Ultimate to verify everything was OK. Then I used NuGet (formerly NuPack) to download and incorporate elmah into the Orchard project. No problems so far.
I'm curious to learn if others are using it with Orchard and what their experiences are. Also I would like to know if the Orchard team has plans for some other error logging solution.