i've just ordered a new dell xps however i've had a dell inspiron 8200 notebook for almost two years now and i have left it on 24/7 for almost the past two years. Only time i shut it off is if i'm traveling to/from somewhere, then i might shut it off. And every once in a blue moon, if i'm away for a long period of time, a one week business trip or something somewhere and i don't take my 8200, i will shut it down. However when i'm home, my 8200 is on 24/7 and i've had no issues with it whatsoever. I have a small/thin latitude laptop for work and i have yet to shut it down as well, when i'm traveling with it, i just close the lid (don't really shut down) and i have it set to go into suspend mode or hibernation or whatever you want to call it.
One thing that i do though for my 8200 is that i have it set so that the monitor shuts off after an hour of inactivity, i don't run any screensaver crap or anything, monitor just shuts off, and i believe that definitely helps in terms of giving the monitor longer life. As for my work laptop, monitor stays on 24/7 as well.........it's a work laptop and the sooner it craps out on me, the sooner i can upgrade to a newer better model............oooops, did i just say that?