Yeah, I have and have had players who roll dice for their own character's decisions that they could choose as players. I have too, especially when there isn't a lot of detailed GM descrition, or it's an incidental detail or something I just don't feel I have access to what the PC is experiencing or would do or prefer. Particularly for characters with (GURPS) Disadvantages I don't think I have, such as behavior imbalances that don't always drive behavior (e.g. addictions, paranoia, short attention span) or senses (e.g. the GM is describing what the group can perceive, but especially if my character is unobservant, distracted, or hard of hearing or short-sighted or something, then I make my own roll to see if my PC notices), and reaction rolls for when I have no clear sense what my PC would think of some people, or whom they'd be attracted to (or just to practice the reaction roll rules which I usually don't have time to think about all the DRMs for as GM), and also just for general arbitrary whims and choices.