I think that being a programmer leads me to forget how much simple omissions in a user interface can lead to confusion. Although not a too serious issue, I've had several people contact me via this WordPress blog to check that the message they sent me on my Drupal based company site had arrived. The contact form on Drupal doesn't have an option to specify a confirmation page stating that a message has actually been sent; it just takes the user back to the homepage.
I noticed this as an issue when trying to place AdWords Conversion Tracking code onto the contact form so I could count leads in AdWords: Because there's no confirmation page, I had to modify the tracking snippet to fire off a conversion pixel when the form was submitted. However, I didn't consider how the issue might effect users of the form.
I wonder how many other, more serious, issues are leading people to abandon my site without ever thinking about contacting me? I guess I should be doing more with all that Google Analytics data I'm collecting…but, of course, I just need to finish this bit of code I'm working on first.