By the 'humming sound', do you mean the fan? The CPU fan should come on when it comes on, and if it doesn't then you are in trouble, from things like overheating your CPU. But don't worry about that. Basically, yes, using your computer does lead to faster wear of the processor / RAM / ROM, but that is in comparison to the laptop being off. What I'm saying is, it doesn't actually matter.
As for rebooting the laptop, I haven't heard anything about not re-booting. In fact, as I said before, having your computer off is always less intensive than it being on. Of course, I don't normally shut down the laptop if I'm just going to be away for 15 minutes, but that's because I have a slow laptop and it takes about 10 minutes just to turn on and load up what I had before, so I don't bother. I'd say any longer then about half an hour would be a good time to shut down.
The only advice is to run the laptop from mains if possible rather than battery. If you're going to use your laptop for prolonged periods without using the battery (i.e. Using it like a desktop), it can be good to use the laptop with the battery out, which increases battery lifetime.
Not really sure how useful this would be hardware-wise, but I would highly recommend crunchbang linux as a really nice distribution that runs quite quickly and has a very fast boot time. Its a little bit more advanced than Ubuntu to work with (read, will need to know linux terminal commands ;) ) but its a very nice operating system to work with if you want to quickly start up & shut down frequently.
Needless to say, Windows 7 will not be very good in terms of the boot time the longer you use it, due to the so called "Windows Rot" caused by changes to the registry. Your best bet with that would probably be to install as few programs as possible.