You can only buy obsolete equipment
OK it's not strictly true, but it almost is. You see a laptop in a shop that you like the look of - let's say it is the Acme X100. The shop assistant knows nothing about it, other than being able to read the limited specification details on the card, so you go home and take a look at the manufacturer's website. There you find that it is not listed, but there is a X101. In other words, the model you are interested in has been discontinued and is obsolete before you've even bought it. Partly this is down to short production life-cycles; most computers are only in production for a few months and there just isn't time for the stock to shift. The exception to this is Apple: when a new model is released the old one sells out within a week or so. Is it something to be concerned about? Not really. Don't assume that the later version is necessarily any better as this may not be the case at all.
The laptop that doesn't exist
The store is selling a laptop that looks interesting. You're the type of person that likes to read reviews before spending your hard earned cash, so you go home and Google it. But you can't find the exact model: you might be able to find something which is nearly identical, or you may just be directed to 'bogus' review sites which in reality are just price comparison sites. What's going on? The answer is that manufacturers will often produce a batch variant for just one retailer, which then enables the retailer to claim that it is 'exclusive' to them. The usual giveaway is a complicated model number; let's say we are talking the Acme X100 again. Look carefully and you'll find that Camet/Corrys/Tisco/PC Warld or whoever is selling the X100-A402 or some such number. These batch variants may simply be a different colour, or they may have a higher/lower specification, they may be old stock or a frustrated export order. Not necessarily a problem, but further down the line it can lead to difficulties. For instance, you might need to obtain new drivers one day, at which point you find that the model simply isn't listed on the manufacturer's website. Even if they have a fancy website where you can type in the serial number of your laptop it still claims not to know anything about it... to them, it simply no longer exists.
Slow slow, quick quick, s-l-o-w
The most expensive item in a computer is usually the processor. Good processors - that is, speedy ones - cost good money, and it is here that manufacturers look to save money on budget models. They do so by putting in what some would describe as anaemic, under-performing processors. In general, you want an Intel Core i3 or an AMD A6 Quad-core at a minimum. Try to avoid the AMD 'C' and 'E' processors and the Intel Celeron.
You want a computer that is flexible, not one that flexes
Another area for economy is the case and keyboard. On more expensive models, cases are made of metal or high-quality plastics. On economy models cheap, softer plastics are used. Press the palm rest area either side of the trackpad - does it flex? What about the keyboard - does it flex when you type? If it is flexing on a brand new laptop, what state is it likely to be in 12 months later?
You may not need extra software
Most laptops come with a 30 or 60 day trial version of an anti-virus program. The idea is that when the trial finishes you will enter your credit card details to buy a full version and remain protected. Or, when you buy the computer the salesperson will try to sell you a copy of Norton/McAfee/Kaspersky or whatever there and then. You don't need it - there are plenty of free alternatives available and they are just as good as the paid ones. Simply uninstall the trial software and download and install a free program such as Microsoft Security Essentials or AVG Free. Likewise with Microsoft Office - they may try and sell you a copy for £100 or more. It's a great piece of software, but new PCs alread come with a FREE version called Office Starter. It gives you slightly cut-down versions of Word and Excel - for many people it is all they will ever need.