Thanks Danisty. Coincidentally I just bought some circular needles today, and was going to report back to round off the topic a bit. So it's great to see your comments updating this thread. I've just finished my introductory task in knitting in the round using magic loop - a pair of take-away coffee-cup cozies. Or wrist warmers, depending on the recipient.
My initial impressions are that knitting in the round is more faffy than flat knitting. Clearly I'm not yet adept with the needles. I was knitting in yarn slinkier and finer than normal too. And on my old needles with the thrashing viper of a cord. So with new knitter-friendly cord, thicker yarn, finessed skills and especially new found encouragement that there are people out there (you!) who knit only with circular needles, and such adventurous stuff, I'm eager to overcome the faff factor. At the moment I'm curious to see how messed up it'll be to have multiple yarns criss-crossing at the back in an enclosed circular space...
So anyway I bought some Knit Pro Zing interchangeable needles. They're 'silver tipped' aluminium needles with 'lustrous' metallic colour-coded shanks. I got all 5 sizes between 4mm and 6mm. The connecting cords come separately and I chose 50mm, 100mm and 200mm cords with little connecting rods to join the cords so I have a range from 50mm to 350mm, hopefully plenty wide enough for a jumper! The cords come with little stoppers so you can keep your work on them while using the needles for a little side project. As Jan had affirmed the cord is soooo much less unruly than on my old nylon fixed needles, so they'll be getting the old heave-ho. The screw thread fitting seems to work fine and is a comforting good length. With such a (necessarily) fine thread there's a risk of cross-threading - mangling up the thread on the screw head or socket - and being aluminium I wonder how resistant they'll be to the socket mouth being opened up after much (mis-) use, but I took the risk because they were the funkiest looking yet proper solid needles I could find in my local shops. I was tempted by the sets in the snazzy cases but the cord lengths offered were mid range (40mm to 80mm) and wouldn't be long enough for me and the needles ranged from 2mm to 10mm and so I would rarely use the smaller ones, so I saved a few bob while in no way curbing my enthusiasm. Other people had reported snagging at the silver tip junction but a quick firtle in the shop and I couldn't feel any burrs, so fingers crossed.