Defaults are no exposure compensation. If your camera is set otherwise, you're probably the one that changed it and forgot.
In my case, even with it cranked to +1 at all times, the 540 significantly underexposes. What is especially annoying:
1) Since it only occurs with the 540, it would make the most sense to dial in the compensation on the flash. But the 540 has a +1 limit to its onboard exposure compensation.
2) Even if the 540 didn't have that stupid +1 limit, it forgets its settings every time you turn it off.
The Vivitar 285HV I ordered as part of a Strobist kit from MPEX came in Friday. I haven't had too much time to play with it, but so far in most situations it blows away the 540 at approximately 1/4 the price (for the flash itself) and 1/2-2/3 the price (for a full kit including flash, batteries, battery charger, light stand, reflector umbrella, umbrella holder, and sync cables.)