Neutral-ground bonding
The panels are wired correctly. There must only be one connection between neutral and ground in the main service panel.
If a subpanel has a bond, then it puts the neutral in parallel with the ground wire back to the main panel -- and this means current from normal loads (that normally the neutral would carry) will travel on ground paths back to the main panel. This includes bare ground wires, conduits, and metal housings. If someone were to touch anything grounded, they could be electrocuted.
This can also mean that the magnetic fields created in the hot and neutral don't cancel each other out, which can generate a lot of interference.
In the worst case, bad connections or other faults can cause a voltage difference between ground and neutral, causing a lot of very difficult to diagnose problems, and making it even more likely to be electrocuted by touching something grounded (anywhere in the house, from any panel).
In short: There must be only one bond between ground and neutral, and it goes in the main panel.
Differences in voltage
The differences in voltage between the two busses is fairly normal. It is likely caused by the transformer on the pole, or by a load in your house that is causing a voltage drop. For the latter you can try turning off circuits to see if it goes away, but for the former, you're pretty much SOL. That said, it's not a problem. Mains in North America is supposed to be 120V +/-5% (so 114 to 126V is acceptable).
The voltage from neutral-ground is also normal. Here is a decent (but technical) article on neutral-ground voltage. In short, it's caused by the fact that over any length of wire, you have some drop in voltage. Since no current flows in the ground wire, there is no drop there and thus you have a difference in voltage. Another source is induced current, which can be caused by wires going through magnetic fields, such as near motors.
In short, it doesn't sound like you have any problems.
I came across this APC product page for Microsol Isolator Modules, which purportedly provide "safe power in places with poor or nonexistent grounding."
This is probably an isolating transformer, which ensures no current can flow to ground, even if you touch the live wires. The only way to get shocked is to touch both the output live and neutral. Requires a rather bulky, heavy, expensive transformer, though.
If I used a bootleg ground in combination with a GFCI outlet, would the GFCI kill the neutral end of the socket and prevent current from being pushed from neutral to "ground" to my equipment?
The main issue with this, I believe, is that neutral and live may be swapped somewhere - this would make your chassis live. There may also be a slight difference in the neutral voltage, due to voltage drop. As such, it's preferable to leave the ground floating, and trust the RCD/GFCI to trip if something goes wrong.
Ground is tied to neutral at the service entrance but nowhere in the walls. Is there some other kind of second circuit breaker or box I could install in my room with a computer and ups that would be more like what's at the service entrance and less like a bootleg ground?
It would be electrically the same as a bootleg ground, really. Unless you added another ground electrode.
When testing outlets at home, I can see the voltage spiking to 1000 volts on my multimeter every few seconds, but only on some outlets (all are single-phase, 220v). What other kinds of voltage regulators will work without ground? Most of my electronics are dual voltage, so ideas including transformers that step down to 110-125v would be fine too.
The best place to put a surge protector is in your main switchboard, because it covers everything and has the best ground. You should be able to get surge protectors specifically intended for here.
Can I hook a voltage regulator up to a GFCI outlet and then hook a UPS into the voltage regulator to deal with nuisance trips from the GFCI and avoid hard drive failure? Can I still get surge protection without ground?
I don't think the surge protectors are anywhere near as effective without a ground. You also need to make sure all the other cables going to your PC (especially coax internet) go through it.
There's a grid of galvanized steel cables, spaced about one foot apart and set into the concrete walls outside which are there to hold up a grapevine. The cables are about the same gauge as a fence, maybe slighly thicker than the copper electrical wires in the wall. If I get good readings on the multimeter, can I use that as a ground? Will it electrocute the neighbor's cats who climb up on the vines or burn the grapevine? What would "good readings" (volts/ohms) be from the multimeter?
If they're connected to the reinforcing bars in the concrete, this could be a good ground. Remember to tie the neutral to your grounding rod - without this bond, it's almost useless.
There isn't an easy way to test that it's a good ground.
Best Answer
Are you sure you're really seeing 500 v, and not 500 millivolts? Those meters can automatically switch scales. – Mark 6 mins ago OMG this was it... im kicking myself now. Everything looks ok im getting 120 between slots, 120 from one to ground and like 2 volts from other slot to ground.. THANK YOU GUYS SO MUCH, i was running around thinking my house was going to explode!