Hmmm... Brewed in a set of 3 glass carboys at 5G, 6G and 6.5G for five years and never broke a one. They glide ok along a linoleum floor if you're careful of how you push them. When you lift, one hand on top, ONE HAND ON BOTTOM. Don't trust friction enough to grab the sides - always always always one hand square on the bottom. Back where I'm from (where, admittedly, the market in these glass things seems to have become self-sustaining), you can buy handles to fix on the top around the neck under the lip. I recommend them, but DO NOT LIFT THE FILLED CARBOY WITH IT ALONE. Empty sure, full no. We are not responsible for the lost floorboards. Lawyers on the release. And even if you use the handle you always have to put ONE HAND SQUARE ON THE BOTTOM. And always ask yourself: do I have to lift it? Is so, ask: what's the least distance from the floor to the shelf? Never underestimate the utility of a trolley with straps.
The milk crate idea is hype, Warren. nice. Good hack.