I spent some time getting your library to work with iOS compiling in-project for an iOS ARC project. In the process I found that the Mongo C library you had was incompatible with more recent versions of the MongoDB services so I updated the C library for Mongo as well. Feel free to grab it.
Update to latest Mongo C driver, work with iOS
Which version of the Mongo C driver is this?
I just released v0.9.5 of ObjCMongoDB which uses v0.7.1 of the driver. Take a look at it, if you'd like!