These numbers can be a little confusing because the dbms you're seeing are actually signal loss off of the original signal. So the higher the number, the more signal loss = less bars.
Now my own testing on Verizon in a large metro area are as follows...
Inside a concrete building's basement while showing 0 bars was -108dbm (I was still able to place a call and it didn't switch to 1x from EV.)
Outside in a wide open area with 5 bars was -46dbm.
About the only time you'll see -0dbm is if you climb a cell tower and launch field trial. Just be careful not to drop your 6800 from up there as it probably won't survive the fall.
Edit: I thought it might be important to note the the signal bars you see on your screen aren't ENTIRELY accurate for all things. Ever notice that sometimes when you have 0 or 1 bar in EV mode, then you get a call it switches to 1x and jumps to 4 bars even though you didn't move? That's because while in EVDO mode, you're seeing the EVDO (High speed data) signal strength. When it switches to 1x for calls or text messages is when you see the most important signal values.
I'd say if your phone says EV next to the signal bars, even though there aren't many, you're getting pretty decent signal anyway. When in remote areas I loose the EVDO and switch to 1x automatically and see 3 or 4 bars.
If it's defaulting to 1x, and you see only 1 bar, then I'd say you have a problem and you'll probably see your signal in Field Trial being past the -160db mark or more. If you're seeing below -100 then all is probably ok.
If this info helped you at all, click on the green thanks button. (I'm tryin' to get mah rep up!)
God I need a hobby......