Like my Dad always says; If you have to read the instructions, it is a poorly designed product.
The problem with new gadgets is that they aren't new... They're the same old gadget with a few new bells and whistles. Don't get me wrong bells and whistles are great. But if you're tech savvy and you've used the predecessor gadget then you're more then likely able to use the new gadget to its full potential. Either right off the bat or really soon after using it. Like cell phones for example, unless you jumped from an 80's style analog phone to a "com" smartphone, you can probably use the phone to close to its full potential right out of the box. So to answer the question of whether I use a manual or not, no I don't use one. If I do end up really stuck then I usually read 3rd party howto's on the subject. I find you get more insight into the problem.
I always read my instruction manuals, but only after I've played around with the device. I don't read it to find out tricks for things that I don't know, because almost always I already know everything about the device and the software before I ever get it.
It's more of a "oh, I'm bored and I have some down time... what should I read?" And then I grab the manual and start reading it.
I read the manual right off the bat, I aways find new things that I didnt know a device could do or do something faster. Like Ryan above I want to use my new device to its fullest.
That is my biggest pet peeve... the first thing I do when I get a new gadget is read the manual front cover to back cover, why get a gadget if you can't use it to it's full potential, or even know how to use it properly? I've had friends before that have really expensive phones and not know how to change the ringtone on it. Like come on people, read the manual!
I often find myself reading manuals if I get bored, like something charging, or initializing. That tends to be the only time I read the manual... or if I get amazingly perplexingly stuck.