Dealer's Choice implies that Billy Ray's ace made him more aggressive, reckless and prone to conflict. While in the first books he may appear like a jerk, later books show that he is smarter than it may appear at first, yet can't seem to shut up when it would be appropriate, an attitude which ends up getting on most people's nerves. Why? His ace drives him towards conflict.
With people like Travnicech and Detroit Steel around, it may seem odd that technology in the books is consistent with that of real life. Modular Man and Detroit Steel's armor were constructed with common materials. Except that it doesn't matter what they are made out of, they work because their creators believed they could work and so their aces made them work.
Suicide Kings. They live all of their life fearing the day they'll turn their card, knowing full well they have excellent chances to either die or become disfigured, and there is nothing anyone can do about it.
The idea that anyone, at any time, can get a superpower, although the chances are pretty low, can be terrifying. Sure, there are some aces that try to use their powers for the right cause, but there are aces who are also gang members, thugs for hire, deranged psychopaths or even petty criminals. Beware The Superman indeed.
Mark's "friends". Not only are they aware of what is happening around them but are forced to act as passive passengers and can only be freed for an hour if Mark wishes so, but Turn Of The Cards severely implies they used to be real people and not just a byproduct of Mark's ace, and were somehow absorbed by it. This people had a life and found themselves trapped in another man's head, forced to watch life from the passenger's seat and even when they are freed, they know it's just for a limited timespan.
Also, the same novel has Mark wondering if Starshine's death has made him more cynical and less idealist. On the other hand, all of Mark's friends care for Sprout, even the Dirty Coward Cosmic Traveller, which implies that Mark's personality has also influenced them. How much of what we see of Mark is his real personality, and how much are the others bleeding through?
You may draw your card at any moment, finding yourself trapped in a nutated body or simply dying. A minor character mentions that one day he simply left work earlier because of a mild headache, went to sleep hoping it would simply pass and woke up with a crocodile's head. Especially if you are a Suicide King, you'll probably wonder at any headache, strange pain or health issue if it's your card turning or just something completely normal.
