If I might add my two pennies...
I have a MSI GT72 with the I7 4870HQ and 980m. Personally, I bought this due to travelling frequently for work, staying in hotels multiple nights a week for 6-9 months of the year.
As Loki said above, performance is a lot closer to desktops these days. Temps on these laptops are also significantly better. Most of the time, I game at around 50C on more modern titles, it's only GTA V and pCars that I have seen higher and even then it's been about 60C, with very high settings running vsynced at 60fps. Although both do dip in certain scenarios but rarely much below 50 and at worst I can't recall dipping to 40. I could actually stop this by dropping some AA or another intensive setting but I'm liking the eye candy. Older titles like Burnout Paradise and Saints Row run around 40C.
I do sit at a desk at times, particularly when playing driving games as I have a G27 but my main reason for posting is to share what I use for comfortable lap play time. Here is a google image search for "
Bean Bag Tea Tray". Honestly, well worth a purchase. I do also tend to stick something like PP3 batteries under the rubber feet for additional space when doing any "serious" gaming but I also have a USB keyboard and mouse plugged in too. When relaxing I generally use a 360 pad.
Obviously, if you spend a similar amount of money on a desktop you'll get better performance but I can't put my desktop (which has now been superseded) in my rucksack and take it away for a week. I also have an inverter so I can game when it's not my turn to drive if the journey is sufficiently long enough and I don't need to catch up on my sleep
Ultimately, if it suits you and you can afford it, these high spec laptops are good machines and these days anyone coming up with the age old adages of "you can't game on laptops" or "laptops run hot" simply is not up to speed on how the technology has improved.