You
can do pretty decently on a laptop, equal to at least the kind of reasonably upper-end desktop that can play most or all current games at max settings at 1080P with room to spare for the future. It's just a matter of price. I can get you there with a desktop for $1000 or less. A laptop is going to be $2000+ and still won't do as well often (lower clocked CPU, 20% or more)
For what Csand describes, I'd expect to pay around $1600-$1700 (from Sager, way more from most others), or what you'd get out of maybe an $800 desktop.
Basically, take this laptop
http://www.sagernote...del_name=NP8298
and with current deals, upgrade to either the R9 M290X or the 880M (880M is considerably faster, worth 15% more overall price tag imo), the 4810MQ CPU, either the 8GB dual channel or 16GB dual channel RAM (8 is fine for now for everyone, but 16 may become necessary later; use your own judgement)
Depending on how you go with the GPU and RAM, you're out between $1559 and $1874, 1784 if you want the GPU but not the RAM, the option I'd go with if you wanted to fall in the middle.
Again, this is for a laptop that can do something in the ballpark of what this desktop can do:
http://pcpartpicker.com/p/3ONqR
That desktop is equal in capability in most respects to the most expensive configuration of the Sager build above. I say most respects, because the desktop has a 3.5ghz CPU instead of a 2.8ghz CPU (not counting turbos which are likely similarly far apart; the desktop one can go to 3.9 on a single core). Add $100 if you don't have a monitor. It's still literally half the price.
Now, this is not a very optimal desktop build mind you. I didn't strive for a best-for-the-money desktop; I aimed solely to replicate the above laptop. For only a few bucks more, you could add overclocking capabilities, enough to get a CPU into the mid 4ghz range. For moderately more money (~$200), you could double, yes double, that GPU's power (that would be an R9 290). Compare that kind of upgradeability to the laptop, where you have to pay $200 just to milk a 15-20% upgrade out.
I could mention SSDs, but either machine could accomodate one. I will note that the money you'd save going with a desktop will free up enough to add an SSD four to eight times over.
Now, I'm not saying either option is right or wrong. If you need mobility, you need it. I may get something like that $1900 laptop soon myself, but if things work out that way, I will actually NEED that mobility, as opposed to it merely being a minor convenience.
For you, it sounds like a minor convenience is exactly what that mobility is. You don't have to get an ATX case and board, either. Form factors as small as mini-ITX have come far enough to give you good mobility, while sacrificing nothing of your ability to house the components you want and do what yo want with them.
Let's not forget upgradeability either. Intel may not stick with the same sockets past the Haswell refresh, and upgrades in general will probably move very slowly from here on out, but in four or five years, you could replace your GPU and extend the machine's lifespan. On the laptop you'll just be SOL, and you'll be wanted that extra power a WHOLE lot sooner, so don't expect $1900 to carry you nearly as far on a laptop as $1200 would on a vastly more powerful desktop.
It's your choice, but those are your options and tradeoffs (I won't discuss reliability - hint: it goes to the desktop by far).