I've noticed what seem to be one or two bugs with the plasma pistol.
The first problems is that, when in cover, Single Shot ALWAYS misses targets. Other attacks, however, always hit. It's pretty much impossible for me to hit with Single Shot while in cover. I should note that I typically dual wield. I'm not sure if it has the same problem while using only one pistol, and you'll have to forgive me for not being able to test it at the moment.
The second problem is that Piercing Shot doesn't seem to affect horde enemies. This is a huge problem, because it's pretty much the only way you can effectively deal with them.
And just as a side note, I've always found the sound effect with plasma pistols to be a little disappointing. It's kind of this little "pew!" sound. I kind of wish it had a more robust"ZANG!" to it, to really make you feel like you're vaporizing enemies. Oh well, in a perfect worls, I guess...