I haven't had any accuracy problems with either of the Act-Labs guns I have.
There are certain games that have accuracy problems, but I think that's an interfacing/emulation/game calibration problem, rather than a defect in the guns themselves.
For the Digital Leisure series, the guns are absolutely dead-on for me.
Same with House of the Dead 2.
I may pick up one of the eReal guns, when they come out, because they will work with my big-screen.
I've even been toying with the Idea of picking up a PS2, solely for shooting games.