I don't give out study guides, but I release my old exams for classes on my class websites (with keys). Without exams being numbered (and sometimes even if they are) there's a chance that an exam gets taken and stored in a Frat or Sorority file... so I just post them so all students have access to them. With a key, some students use them as study guides.
Sometimes, like Vanadium, I'll use old questions over again (and yes, students will still flunks those)... although I've never used exactly the same test. Often, I just change a word or two, especially on long multiple choice tests -- for example, changing the question from asking about frequency to asking about wavelength completely inverts the correct response. On problem-based tests, I'll often use the same geometry, but change the charge distribution slightly, etc. (With this kind of similarity, it covers my ___, err... it lowers the chances that students complain about tests being "unfair" etc. -- and when my students still fail an EXACT problem, they usually cower in their chairs, improve their work and study habits, or drop the course.)
Maybe it's hand-holding (maybe not). It's better than I got (at a small liberal arts school). I think SOMETIMES professors posted an equation sheet if one was to be given during the exam. But that was in the days before classes had internet sites and ways of easily storing/posting these materials, so who knows what my professors may have chosen to do with those tools available.