Have never had a problem when taking the appropriate precautions.
As an almost always battery user, the clean power "straight from battery cells" thing breakonthru mentions which avoids all conversion, voltage step-up/down, power ground loops, etc, certainly feels good and may avoid some noise problems, although how much it actually matters will depend on the design of the gear and the particular situation.
But do take the appropriate precautions and don't blow your shit up!