I know you can take screenshots with Android 4.0/Ice Cream Sandwich, but I discovered a week or so back that, having upgraded my HTC Desire S to HTC Sense 3.0 (on Android 2.3.5) I can now do this without an ICS upgrade!
Here it is from the horse’s mouth: it seems all you have to do to take a screenshot on your HTC device is hold the power button and press the home button. Your screenshot will be captured and saved to your gallery.
I actually took my first screenshot on my Desire S following the upgrade to HTC Sense 3.0 by accident!! I was on a website in the browser and pressed something that made a message come up “Screenshot saved to Gallery”. What!? Screenshot?
Yes, it turns out you can take a screenshot on HTC Sense 3.0 (and presumably HTC Sense 3.5). I have since got myself an HTC Evo 3D (which comes with Sense 3.0) and verified that the same process works there, the only difference is that it saves to “Camera Shots”.
Much thanks to Andrew Girdwood, whose post “How do you take a screen shot with your HTC Sensation” I came across on a Google search as his comments section was where I first discovered the answer.