My worst dice rolls ever were in one session of Red Hand of Doom. I was playing a meleer with a fairly decent attack bonus (+16 to hit before PA, I think the PC was L7 or so) and in six hours of mostly running combats, I didn't hit once. I think my highest attack roll was a 4, and that happened to be against a bad guy with decent AC. There were AC 17 and lower foes in that part of RHoD, I just rolled 1's whenever I faced one. It was frustrating.
After that session, I dubbed the die I'd been using the Yellow Die of Doom and refused to use it again as a player. However, it seems that when I GM, the Yellow Die of Doom rolls sub-5 80% of the time, but the other 20%, it rolls nat 20s. I generally gave players the choice as to whether or not I used it
My wild mage, on the other hand, always had very, um...
appropriate dice luck. In her first wild magic field, long before she took the PrC, she got every single possible good outcome, and none of the bad ones. At L15 she (foolishly) tried to kill a CR 20 beholder-type BBEG by herself ("Enemy of the Magic! KILL!"), and made about 10 consecutive DC 36 saves before bombing one (with the buffs she had active at the time, this meant rolling 17+ or so - needing high rolls but not nat 20s). On the other hand, her Teleport dice came up with assorted errors on a disturbingly frequent basis. She didn't mind - it made it more interesting - but more than one party member refused to teleport with her after a while