It isn't that I don't trust carbon stems, I just don't see much of an advantage they have over metal. I do see an advantage of a Thompson seat post though. A Thompson seat post weighs about the same as a carbon seat post and they won't get scratched up when you adjust them.

As far as my wheels, I have Topolinos ATR 3.0 wheels which have carbon spokes combined with Kevlar and they have aluminum rims. They have the best ride quality of any wheel I have tried. The carbon deadens vibration really wheel. I don't expect to have any reliability problems with them unless I am in a crash and break the wheels. I like that they have aluminum rims. I prefer an aluminum braking surface over carbon and if the rim is damaged, they are cheap to fix.

Oh, I also have carbon handlebars because I like the shapes that can be molded into which I don't can be done with aluminum.