I've never had an issue getting to the bottom of my bottles with a standard bottle brush - and the only reason I ever need to do that is when I've left them lying around with HEED in them. 
Normally the opening is as big as a drinking glass and they're as easy to wash as a drinking glass. If you don't like to put plastics in the dishwasher, then a wet dish rag or an ordinary bottle brush will reach the entire inside.
The valve can get funky (again, usually if I'm less than diligent about immediate rinsing after a ride), but soaking the lids with a denture tablet takes care of that. And the "clean bottle" doesn't look like it offers any special kind of valve.
I saw something about a bird feeder with a removable bottom the other day, and I thought that was a great idea. I just don't see that it's necessary for bicycle water bottles. Considering that they almost always drip a little bit out of the top lid where it's only road sloshing and not gravity forcing the water out, it just looks like another opportunity to leak sticky stuff all over my frame and bottom bracket.
ETA - I've also hesitated to go to steel because of the stiffness - not because I don't think the cage would flex enough (I'm sure it would) but because I'm afraid I'd have trouble holding on and dispensing water. If you just open the valve on a regular bottle, gravity only does so much, you really need to squeeze it to get water quickly enough. So I would also like to hear from some people who use SS bottles.
Last edited by OakLeaf; 08-10-2010 at 04:12 AM.
Speed comes from what you put behind you. - Judi Ketteler