I used to use a passive Morley ABY, I never thought it was enough to care about, but I haven't tried it during recording. I also don't use a lot of gain or distortion, which would make it worse.
As to the other question, the signal doesn't get "split", in the sense that half goes to each amp. Each amp just "sees" whatever voltage the guitar puts out, and reacts accordingly.
Plugging into two amps drops the impedance the guitar sees, which drops it's output bit, and can effect tone. So each amp will be a bit quieter, but maybe not so you will really notice, and certainly not by half.
If you run out of a processor, or use pedals without true bypass, or have active pickups, you may not notice the difference at all. These things can generally drive various impedances with no loss of signal.
This won't solve the problem of pops when switching, though.
An active box designed for this purpose will also solve your problems. Radial makes one, but at $230, it ain't cheap. There may be others out there.
