My little Acer Aspire One netbook is increasingly feeling underpowered, so I'm contemplating getting an ultrabook.
I have a full desktop computer with a decent monitor, but that sits upstairs and only really gets used for graphics or anything else that needs grunt (e.g. R), running video and audio downloads, for managing my web sites, and as my primary file server - it has a pair of RAID-1 1TB drives and is backed up regularly.
When working downstairs, or in the Bodleian library or in cafes, I've been using a little netbook, a first generation Acer Aspire One, which was originally intended just for travelling. It's a nice little machine, but it's been a bit frustrating, largely because the SSD is incredibly slow on writes: sometimes it locks up completely for five or ten minutes, and a Fedora distribution upgrade can take 40 hours or more. The slow SSD interacts badly with having only 1GB of memory. Also, the screen is small and the battery lasts only just over two hours.
I bought a fast SSD and extra memory to upgrade the machine, but that failed when I couldn't get the motherboard out - the screws had corroded on.
So I've been thinking about getting an ultrabook. The main requirement here is that it be light, ideally no more than 1kg, and robustly built, so the best candidate seems to be an Asus UX21a or, since that's not yet available in the UK, perhaps an 11.6" Macbook Air. The Air works nearly completely with Linux and is what Linus Torvalds uses.
The downside is that the Macbook Air is rather expensive, around £850, and the UX21a, US$1000 in the US, is likely to be as or more expensive in the UK. So this will probably be the first thing I buy myself if I manage to get a day job - especially if I can salary sacrifice it.