Desktop-replacement laptops are a great alternative to owning a full-sized PC. They have the advantage of being portable (or at least luggable) and many of the latest models offer performance in line with the fastest desktop PCs.
The most important consideration when choosing a desktop replacement is probably screen size. You'll need to ensure it has a large display if you intend to use it in the long-term, so plump for a 17-inch or 19-inch model, as anything smaller could be quite uncomfortable. For extra flexibility you should consider the Samsung M70, which has a detachable 19-inch screen. This has its own stand, which raises the monitor to a more readable height.
Next you'll need to ensure the laptop provides enough performance to cope with everyday tasks. It's always a good idea to opt for a slightly faster laptop than you think you may need, as performing a future upgrade won't be straightforward.
Some desktop replacement laptops use components you'd normally find in full-size PCs. Many, for example, use desktop processors, but although these are very fast, they have the disadvantage of being noisy and hot, and will invariably be a huge drain on your battery. Laptops with dedicated laptop CPUs tend to be slightly slower, but they have fewer of these downsides. If possible, try to buy a laptop with a dual-core processor, as these provide excellent performance and are usually more power-efficient. The Asus A7J is a great example of this.
Laptops have recently come of age with their graphics-processing abilities. They can now rival dedicated desktop gaming PCs thanks to the advent of fast mobile graphics processing units (GPUs), and some models now have dual graphics cards for running the most demanding of games. As a rule, keen gamers should ensure their chosen laptop has a screen with a high enough resolution to take advantage of these fast GPUs.
One area often overlooked is connectivity. Some laptops have as few as three USB ports, so you'll have to do some cable juggling if you have lots of peripherals. The Dell Inspiron 9400 is a great solution for USB junkies, as it has a whopping six ports.