Chip - You are correct about the voltage drop, especially at lower amp
ratings.

DISCLAIMER/WARNING - Working on a standard certified aircraft requires
an appropriate FAA issue technitian's (not pilot) license.
Experimental aircraft is less strict but I still recommend someone
looking over your shoulder. 'Nuf said.

All standard breakers use a resistive element which heats up by the
current flowing through it. If there is enough current and it gets
hot enough, the breaker will trip. As anyone who has worked with home
electrical resistive heating systems knows, they draw quite a bit of
current, which translates into high resistance, which translates into
a voltage drop. This is E=IR stuff. If you are trying to heat your
cockpit (or your house) this resistance is good. Otherwise it is
bad. I made a presentation at the last convention in Memphis (http://
geocities.com/jhderosa/aviation/presentations) which touched on this
subject.

The standard aviation type Tyco/Brumfeld or Klixon breakers drop
0.25Vdc for the 5A model and 1.1Vdc (!!!) for the 1A model. If
gliders had generators providing a constant 13.6Vdc, this wouldn't be
much of an issue. But with fixed capacity batteries on board, it is
an issue.

There are some options.

1) Don't use multiple small breakers for each item. Rather use one
large single master breaker (like a 5A or larger) as you can probably
afford to loose that 0.25Vdc.
2) Use all-electronic breakers (http://aircraftspruce.com/catalog/
elpages/circuitbreakers.php). They only drop 0.1Vdc at any load
rating.
3) Use the neat little R59 series of breakers from NTE (http://
www.sourceresearch.com/nte/r59.cfm) which only drops 0.15Vdc at 5A.
They are a direct panel replacement for glass fuse holders.
4) Stick with glass fuses if your glider came with them. Strictly
speaking, they are not to be used in standard certified aircraft.

As to whether or not breakers will trip fast enough....yes breakers
are slower than glass fuses...but is this an issue? Remember that
all powered airplanes from A380's to Cessna 150's use breakers. The
primary thing that you are trying to protect against is an overcurrent
condition like a dead short. What you are protecting is not the
electronic gizmo, but the power source (the battery). A dead short
won't harm the electronic gizmo (unless the short is inside the gizmo
which means you have a warranty problem). However, applying a dead
short to a battery can catch the plane on fire which is considered
rather bad. It can also fry the wires which is equally bad. Any
breaker will trip quickly enough to prevent damage to wiring and
batteries which will save your bacon.