[Taqwus]

I have had the Chalice in games for many, many, many turns (scores, really; I play /really/ slowly single-player to have time to experiment with powerful summons, goofy configurations and fun magic) and not once seen the knights attack.

Some artifacts are far more dangerous. The Gift of Kurgi comes to mind; both times I tried it, the commander Lasted less than ten turns before the horrors came and ate him. The Horror Harmonica is dangerous; when it Calls Horrors, the arrive next to the caller and are not particularly friendly. Personally, I like the Chalice; it's useful even when you have GoHealth because you're not necessarily fighting in your own dominion.

The Ark is dangerous if you bring it into battle with anybody but priests and sacred troops; I'd keep it on a stealthy commander, and switch it to the lab if it were ever in danger.

Some downsides are nasty but not mentioned. Asfetik's Armor, for instance, cannot be removed; nor can Amon Hotep (awesome helmet; Prot 30, plus a MR bonus, plus a mummy-generating activation). The Crown of Overmight might also be this way. Magebane horror marks you (but not severely; attacks seem rather rare... and besides, you're wielding *Magebane*, the sword that automatically does 100 Fatigue unresistable per hit), as does the non-artifact Robe of the Archmage (minimal prot, but reinvigoration plus +1 to all magic!). The Banefire sceptre is fairly strongly horror-marked I think.

Note that even if you play with immortal commanders, horror marks and curses will stay with them when brought back. I'd rather use a cheap indy commander if I'm going to risk the ire of the forces of darkness...