In reply to MattJP:
Hi mate,
we have a Littlelife Voyager. Older version of this:
http://www.littlelife.co.uk/html/child_carriers/voyager-s2.html
Our daughter has been in it from about 6 months. She was in it every day in all sorts of weather when we toured Europe in our campervan last year.
I'm a stay at home dad and I take her everywhere in it. She loves it, falls asleep easily and for me, it has heaps of storage and the frame and straps are as good as any rucksack I've ever had. Easy to adjust between me and the other half when on the move (Anna is 5ft 10, I'm 6ft 3).
It has been up Snowdon twice, up the Ben, heaps of Wainwrights and her favourite, Cats Bells!
I'd highly recommend it, I was going to get a Macpac but as with the rucksacks, I didn't like the shoulder straps. Picked ours up in mint condition for £60 on fleabay. Only thing I'd recommend as an extra, is the little chin pillow and the sun shade. Don't bother with the waterproof cover, Daisy wears a Bushbaby all in one and doesn't seem to get wet or mind the rain. The rain cover makes her feel quite claustrophobic and actually Isn't all that breathable.
Babbled on enough, whatever you buy, it is a great way to get the kids out and they really seem to love being higher up.
All the best, Den