It is sometimes hard to reproduce errors because I don't know what URL users hit to get the errors. Is there a log somewhere that tracks errors along with info from the http request that spawned the error? 

If not, is there a way to set this up easily, for example a module that does this? 

I'm actually working on this exact problem as I write this.  I should have a solution in the next day or so and will post it here.

Filed and Patched: http://orchard.codeplex.com/workitem/19401

Very nice, thanks for contributing this patch! I'm going to try this out this week.