Yeah, mine is on about 10-12 hours a day on average, whether for work, downloading overnight or whatever.. no problems. Same with my old i8500, I used it all the time for a year and no ill effects, as mentioned, the only worry is if you are on battery the most of that and wearing down your charge/ discharge cycles more quickly.
i wouldn't worry as long as you have a warranty and you don't keep it on too long it hot conditions... as long as the temp you are using the laptop in is good enough to keep the temps at good levels there should be no problems... your pentium-m runs pretty cool anyways so i think your safe too... if you want you can always extend your warranty later if you think that's in your interest, just do it before your current one runs out
My Compaq is powered up about 8-14 hours a day. I have had it almost 3 years and it performs as good or better now than when I purchased it. Most electronics components break during power up, so the less times you power up the longer MOST things will last.