Laptop for me means no wires, and I love that. Speakers / mic / mouse / screen all built in and can be tidied away / used somewhere else in 2 secs.
Wireless printing, and wireless connection to the hifi for playing your music collection is now possible - esp. easy on the Mac.
If you don't need it for super high tech gaming, but ordinary Web surfing / word processing / address book / calendar / e-mail etc. then a low-spec, cheaper machine would be fine.
With regards to H&S / ergonomics, I run a 17 inch laptop, so huge screen, but even if it was smaller you could plug in a larger screen instead. Full-size wireless keyboard / mouse are also available.
I would not hestiate to recommend a Mac over a PC. You won't spend your entire life battling viruses and spyware and rebooting. Plus you'll feel smug as the hardware is so elegant and the interface is beautiful, and it'll be an absolute doddle to play with your digital photos etc. You also won't need resident IT guru every ten minutes.
Apple do laptops from £700, a new 'cheap' computer you connect up to an existing screen / keyboard / mouse so you can recycle your PC for £340 and two all-in-one computers (PC with screen) - a large CRT one for £550 and a thin LCD one for £900. New flagship store in London if that is useful too.
Worth their weight in gold, I promise.