There seem to be quite a few people who insist that their laptops are "just as good as a desktop." My carefully considered evaluation, for most, in the gentlest terms I can muster, are "These people are idiots."
A laptop keyboard is necessarily laid out to minimize the space, instead of to fit humanoid fingers. Layouts vary from one manufacturer to another, although I'll grant that they're becoming more similar to each other. On all that I've seen, the key covers fall off in about a year, but that may be because the ones I see don't get used much, so maybe the keys get dusty. ...
Using a pointing device is sufficiently helpful that nearly all laptops now include both the wobble stick - which is too slow for good control - and the touch pad - which requires you to adopt a contorted typing style to avoid the random jump effect.
Processing speed and component capabilities in decent laptops are adequate for many applications, but are far behind what's in most desktops for "heavy duty applications." Serious gamers (or even gaming wannabees) DO NOT USE LAPTOPS. In my opinion, even Photoshop Elements bogs down, and the full CS suite on a laptop would run, but would (personal opinion) be ridiculous.
Any failure on the motherboard generally means junk it and get a new laptop. In laptops, virtually everything is on the motherboard, including graphics, sound, connectivity (ethernet/firewire/USB) components, etc. In a desktop, even if a sound or graphics card is integrated, if it fails you can plug in a separate sound card and ignore the failed one, but on a laptop most people would buy a new laptop.
The most annoying feature I find in laptops is that laptop hard drives actually operate at a about a fourth (at best, 10% in many) the effective speed of even mediocre desktop machines. High rpm disks are only rarely used in laptops, since the Coriolis demon would make them disintegrate if the device is moved while the disk is running. While the specs for read/write time, random seek, and intial seek are comparable, to protect the disks laptops "park" the heads frequently, so nearly every disk read/write is "from park." The lag, even in Word - which is not "disk intensive" - is noticeable if you're accustomed to a decent desktop.
If you absolutely do not have space for a desktop or if you must take it with you then a laptop is obviously what you need.
I have a laptop to take along on trips and to campsites; but I plug in a USB "transmitter" that lets me use a standard desktop keyboard and mouse (optical) anywhere within about 60 feet, with no wires1. The keyboard can sit on my lap if needed, and the arm of the chair can be a mousepad, although I generally set up something more comfortable.
For places where you can't set up useful accessories, having a laptop and learning to "live with" its peculiarities probably is better than having nothing, but it's NOT A DIRECT REPLACEMENT for a desktop machine, unless your use is extremely "simple."
1 The keyboard/mouse I'm currently using is a Microsoft "business kit" that should be available fairly widely, and was about $50(US). In typical Microsoft fashion, the mouse uses a single "AA" battery, and the keyboard, where there's lots more space for a battery, uses a "AAA." Battery life is pretty good and wouldn't be a big hit using "throwaway" batteries, but the different sizes do make rechargables less convenient than necessary since separate cycles (or separate chargers) are advised.