I have particular interests in stamp collecting and geography. I am currently spending most of my time correcting errors on random pages, however - it's an impossible job to fix them all but I enjoy making small individual improvements.
Most of my error corrections deal with malformed citation templates. Some of these errors have always been invalid and some were formerly valid uses of templates which now cause errors due to changes made to the module that interprets the citations. Here's a list of the major edits to this module - the links point to the talk page summaries of the changes made to the module.
Some citation errors are hidden by default and the error messages can't be seen unless you have set your personal style sheet to show them. The request for comment that resulted in the decision to hide these error messages can be found here.