I recall a part near the start of "2001: A Space Odyssey" where there was a brief section about how people from Earth usually ended up making fools of themselves for their first few weeks on the Moon base. Same mass... but not as much weight, and thus, not as much grip.
(Near the start of chapter 10 if any of you have a copy and want to find the passage.)
However, with that said, I think any human who'd spent enough time travelling between worlds would be familiar with the difference between mass and weight. Not every world has Earth strength gravity. Some are less than "normal", some more so. Not to mention the quirks of a ship's artificial gravity.
After enough worlds, you'd get used to the difference.
Actually, on the last 'clave I believe, I talked about why this made the lasgun a practical weapon for the Guard. As gravity is one of the main forces on a projectile's trajectory, and a regiment can be sent to almost any planet (with widely ranging gravity), a solid projectile weapon would be much harder to use at any real range.
Lasguns, being almost unaffected by gravity, are therefore a much more practical choice.
But that's not really the point in question. Anyway, I'd say someone who'd been wielding the sword long enough would be familiar with its quirks. However, if anyone else were to pick it up... well, I can't say for certain (you'd have to ask astronauts, or just anyone who's experienced zero grav), but its unnatural combination of mass and weight might well make it dangerous.
