So, what are some obvious signs that it's time (or past time) to put on new brake pads on V-brakes?  Is there a "minimum pad thickness" to watch for, or is it something more obvious, like what I may be experiencing:
 
I recently noticed that, no matter how hard I squeeze on the rear brake lever, the bike doesn't really stop when I try it only using the rear brake, and I was having trouble slowing down in left turns with my left arm extended to signal.  I tried adjusting the cable length, to no avail... then I noticed that when I squeeze the brake, the point of the cable where the rubber grommet is just beyond the little metal bracket that goes over the rounded metal thingy is meeting the other arm -- as in, THERE IS NO MORE TRAVEL TO BE HAD -- the brakes are squeezing as far as they can go!  
 
I realized at this point that, perhaps after two years and 12,000+ miles, it MIGHT be time to put new pads on...  there's not much thickness left of those original pads!!!  
 
PB
 

What's interesting is that I didn't really notice it until I switched back to the original Alex DA16 wheels from the Velocity Thracians...  the Thracians are slightly wider, and were still stopping OK...

Ok that wheel changing comment has be back to wondering what is going on.
"I tried adjusting the cable length, to no avail... then I noticed that when I squeeze the brake, the point of the cable where the rubber grommet is just beyond the little metal bracket that goes over the rounded metal thingy is meeting the other arm -- as in, THERE IS NO MORE TRAVEL TO BE HAD -- the brakes are squeezing as far as they can go! "
Does your brake look like so?

And that rubber grommet you speak of it the little black accordian type thing between the two arms that the cable goes through? If so I believe it should compress just fine, at least it does on my xtracycle.  
 
Mind you with that many miles you still might need new pads, probably need new pads. They are not too expensive even if you need a whole new holder and not just the inserts. $5-10 for a pair of inserts $10-20 if you need the holder and pad.
 
 
 

hm.. yeah I guess it is time to change the pads then. Unless you had washers out of order there isn't really a way to adjust them other then the cable.  
I guess I just always have had wide rims because I never have seen that fully clamped and still not stopping thing. I love big fat tires, for a big fat me  
 
Edit: those pads/padholders look like they take just a new pad insert. Not sure if the ones on your bike do also but that makes it really easy. Well should anyhow but you do have 12,000 miles so they may or may not take some effort to get out.

Now the $64 question, can you skid either wheel with just the application of the one brake? You know so you can pass inspection should DPS State Troopers pull you over because of your funny-looking bike.