I've got a 5 gallon carboy that came with my beginner's kit. It gets use every once in a while bulk aging a beer that benefits from bulk aging (Brett Saison right now). It lives in a 25L bucket. Being tapered a little like most buckets, the bottom of the bucket hugs the carboy nicely - I think it actually rests a couple centimeters above the bottom. There's no reason for me to take the carboy out of the bucket in most circumstances and very little chance of getting hurt if it breaks. Heck, I could even salvage most of the beer in that case by putting some kind of filter (for glass shards) on the end of my autosiphon and siphoning the beer out, though it'll probably be a bit oxidized.
I have little interest in participating in the glass carboy sweepstakes so I can watch my krausen grow, but with the carboy in a bucket and an old t-shirt wrapped around the top, it doesn't worry me as an occasional long-term secondary vessel. No thanks on milk crates - I could see a bunch of ways that could go wrong - but a bucket is good by me.