One of the CB'ers mentioned how much he likes log4net, and I just had to 2nd that notion.  Thanks to Paul, I've started using log4net for all my logging needs, and it's amazingly lightweight and very configurable.  I've had to use the new EntLib for data access and configuration for a couple things, and to be honest, it just felt like bloat-ware.  Config files, config files, everywhere.  log4net is very simple to use and set up.  I like to think of logging as "inline comments on steriods".  I do also like what Ron Grabowski said (check out the comment thread here) about abstracting out your own logging interface for your project, allowing you to plug in and swap out logging engines (log4net, EntLib, etc.).  I'll probably try and do that on my next project.

BTW, log4net has a ton of documentation that I've used quite a bit, so go check it out!