Apple says that the Macbook Air is a ‘no compromise ultra-portable laptop’.

That’s certainly true in some ways: the unit measures less than 2cm thick (0.76in) at its thickest point, and even the somewhat-miffed Sony hasn’t really disputed Apple’s claim that this is the ‘thinnest laptop in the world’.

Sony does win on weight as its Vaio TZ weighs just 1.24kg, compared to the Macbook’s 1.36kg. However, the Macbook Air has a bigger screen – 13.3in compared to 11.1in for the Vaio.

Ultimately, though, Apple’s engineers know that there’s more to good design than just a spec-sheet full of numbers. It’s the sheer elegance of the Macbook Air’s slimline design that catches the eye, and when you feel how comfortably the machine balances in the palm of one hand you can’t help but wonder if your credit card will stretch to buying one.

There’s no doubt that Apple has hit the ultra-portable nail right on the head. But shrinking the unit down to this size has inevitably involved compromises in other areas, no matter what Apple says.

The most obvious compromise is the processor. Apple got Intel to produce a customised version of the Core 2 Duo for the Macbook Air, but the only models available at the moment run at a modest 1.6GHz or 1.8GHz, priced at £1,199 and £1,389 respectively.

Anyone looking for a powerful laptop to replace their desktop PC or Mac should probably look elsewhere as the Macbook Air simply doesn’t have the raw horsepower for that. Even so, it is more than adequate for running ordinary business software such as Microsoft Office, surfing the web and handling your email.

It’s got 2GB of Ram and, while the 80GB hard disk is pretty small, the Macbook Air still compares favourably to ultra-portable rivals such as the Vaio TZ, which hits a top speed of 1.33GHz with 120GB hard disk and costs a hefty £1,799. A 64GB solid state drive version is available for £2,028.

You will, however, probably end up spending a bit more on optional extras for the Macbook Air. The ultra-thin design leaves no room for a DVD drive at all, so watching DVDs is out of the question – unless you pay £65 for the optional external DVD drive. Interestingly, using the included Remote Disc application you can install software on the machine over a wireless network by using the optical drive of any other computer you have available, PC or Mac.

There’s only a single USB port for connecting peripherals, with no Firewire or Ethernet at all. The loss of Firewire means you can’t plug in a DV camcorder, while the lack of Ethernet is just daft.

Apple’s argument is that the Macbook Air is meant to be totally wireless – fine when wireless routers never fail and the entire world is one big happy wireless hotspot, but until then we still need Ethernet occasionally. So budget an extra £19 for the USB-to-Ethernet adapter as well.

And it wouldn’t be an Apple product if there wasn’t one utterly inexplicable design decision. In this case it’s the battery – or, to be precise, the fact that the battery is sealed inside the unit so that you can’t extend your working time by putting in a spare battery when the original runs down – after about three hours with the Wifi running.

Omissions such as the lack of DVD drive and the non-replaceable battery will mean that the Macbook Air simply won’t be suitable for some people. And it’s not powerful enough to replace a desktop PC or Mac.

However, the sheer size-zero slimness of the unit is hard to beat, so if portability is your top priority then the Macbook Air could be just what you’re looking for.