In tough economic times, luxuries are the first to go. But how long has it been since you regarded your computer as a luxury? Most of us treat them as necessities: workhorses for carrying out essential tasks, entertainment centres for watching videos and listening to music, and gateways to the web.

Fortunately, new computers no longer cost an arm and a leg. Increasingly, bargain hunters are turning to netbooks, the new generation of low-cost, lightweight laptops, when they want to get a new system on the cheap. Initially perceived as niche products that would appeal to technology enthusiasts with a bit of spare cash and business people looking for a truly portable machine to take on the road, netbooks (also known as mini laptops) have now gone mainstream. All the major laptop brands have now entered the market bar Apple - and, if the rumour mill is to be believed, the Mac maker is planning to launch one at some point in 2009.

Initially, industry spectators suspected that suppliers were only interested in launching "me too" products to compete with Asus's original Eee PC, but there's a good deal of diversity between the various models in our Top 5 chart, particularly with regard to battery life, build and price. And any suggestion that there's no mass market for these products has been blown away by statistics from research firm DisplaySearch. The company has reported that worldwide netbook sales increased by 160 percent between the second and third quarters of 2008 - reaching an impressive total of 5.6 million units.

With online retailers such as Amazon heavily promoting them in the run up to Christmas, and mobile operators including Vodafone, O2, Orange and T-Mobile supplying the products ‘for free' with 3G mobile broadband contracts, it's likely research firms will be able to report another big surge in shipments in Q4.

But is a netbook really the best option if you're on the lookout for a low-cost computer? Prices have been edging upwards rather than downwards since Asus ignited the market in 2007, and the promises of free laptops with 3G broadband don't always stand up to scrutiny.

Add up the price of a mobile broadband contract over 18 months or two years, and you could be paying over the odds for a system that turns out to be uncomfortable to use for prolonged periods. Netbooks' compact keyboards and small screens are not ideal for sustained use and, given that many premium models are more expensive than the cheapest full-sized laptops, it's worth doing your homework before you buy into the hype surrounding this product category.

If you look at the specs of the models in our Top 5 netbook chart and compare them with those in this month's sub-£500 laptop group test, you'll see big differences in performance. With a mini laptop, you're likely to get a single-core Intel Atom processor, 1GB of RAM, an 80GB hard disk and Windows XP. With a ‘proper' laptop, you're looking at a dual-core chip, 2GB of RAM, Windows Vista Home Premium and a 250GB hard drive. With the battery lives of these so-called low-end models now approaching 4 hrs, these really are good deals.

It's likely that manufacturers were encouraged to drop the retail prices of full-sized laptops to compete with netbooks, which means this new category of computer has had a positive impact for buyers, even if you never plan to purchase one.

One thing's for sure: the evolution towards smaller computers will continue. But think before you get out your credit card. Even at low prices, most netbooks should be regarded as a second or third computer, rather than your main system.

Pick up the March issue of PC Advisor, on sale today, for our full laptop round-up.