I've had my 6600 for a few years now. When my DH brought it home I was very busy working on a couple of projects with deadlines. So it sat in the box for a fortnight.
When I started to use it I wasn't sure if I'd made a mistake in buying it. After a few lessons and lots of sewing I now couldn't imagine life without it. As you said it's not a machine you want to be carting around. It is quite heavy but that's because it's made of metal.
I have a Janome 5024 that I cart around to classes & group. While it is a good little machine I only use my 6600 at home as well as my 10000 for embroidery.