I bought a second hand Graco tandem for £25.00 from my local paper and it was fantastic to use-I really recommend tandems v side by side-I dont know anyone who's had one whos got anything constructive to say about them-they are simply too wide!!
Mine lasted well over a year!
Have to disagree, dropinthe, I borrowed a tandem when ds2 was very tiny, and ds1 (then 2) hated it. He still talks about it now and again and it was 2 years ago. He said he felt like he was all on his own at the front, and its true that he did seem to be miles away. They're a beggar for getting up high kerbs too, the chassis seems to be really weak and it felt like it was bending in the middle.
So I bought a second hand side-by-side Graco one and they both loved it as they were next to each other. They're designed to fit through shop doorways, especially the ones that take wheelchairs, but they are a bit cumbersome in clothes shops where the racks are crammed in close.
I wouldn't recommend spending a vast amount on one as they only get used for a few months before the toddler decides to walk everywhere, but they are popular second hand so good makes keep their price well. I actually sold mine for £5 more than I paid for it as the buyer didn't bother haggling.
I've got a Graco side by side which cost £100 new. It's not as easy to push as the Mountain thingy (which I thought was a bit wide) but I used mine every day with lots of walking for about 15 months. Will have to get it out of the garage again when number 3 comes along.