I bought a Samsung 5 series ultrabook last year, it was about £500 and is very light and pretty quiet, I mainly use it for Word Processing and web browsing and am very happy with it. We've had an Imac for a few years and I just don't feel the love for it at all, especially Word for Mac, which is pretty poor compared to the Windows versions, but we do all our Itunes, Iphone syncing etc from that, so no experience of any of that on the laptop. It doesn't have a DVD drive though, that is one thing to watch out for on lightweight laptops if you want to watch films.
After using pcs/laptops for years I made the jump to a Macbook. I wasn't totally convinced at first - it affected me more as I use a lot of Microsoft in my work, but I got used to how Macs work and think they are brilliant now. As you have an iPhone the syncing works nicely with music etc. Only downside is you will have spent a few quid more than if you bought a laptop!
I'm no techie but as you've got an iPad, iPhone and iPod, it makes sense to get a MacBook so everything syncs nicely, plus you're so used to Apple anyway. PC world are doing a cashback thing on MacBooks at the moment.
I had a Sony Vaio (VERY noisy) up to now. I like Apple a normal amount but by no means a slave to them - got an ipad, iPhone and old iPod. Use a PC at work.
I mainly want a new laptop for word processing (I write lots), listening to music on and watching stuff on. My priorities are that it be light and quiet. I doubt it'll be going out and about as my iPad goes everywhere with me.