Judging by some of the entries I've seen in our photography competition, especially last month's landscape theme, it looks like some people don't know how to correct a tilted horizon. I covered this very topic in a previous tutorial, but only in Photoshop Elements and other basic photo editing programs. However many people have the full version of Adobe Photoshop (a few may even have paid for it...), and the method for correcting tilts in this program is very different. It has no easy tilt correction tool; instead you have to do the process manually using layer editing.
He's the example shot I'll use. As you can see, the sea has developed a bit of a slope to the left. Great for waterskiing of course, but not so good as a photograph.