Before we answer the question, we need to distinguish between two terms up front: shills and proposition players.
The difference between the two is that a prop player plays with his or her own money, while a shill plays with house money. These are both "house" players who participate in order to try to keep the game going so that paying customers won’t be intimated by sitting down at the table. Most players don't feel comfortable playing in a game unless it has at least six or seven players, so a house shill or prop can make the difference between keeping a game going or being able to start a new table.
Since both shills and props are employees, each is paid an hourly wage to play; sometimes they'll even be eligible for medical and retirement benefits through their employer." (Our own Anthony Curtis used to be a proposition player.)
To answer your specific question, shills are virtually non-existent these days. One long-time dealer we queried replied, "The last time I saw a shill stack was in 1989 at the Sahara." What you're much more likely to see these days is a "proposition" player, although rarely in Las Vegas, at least not in the traditional sense. However, as the initial wave of poker hysteria recedes, we did recently come across an ad from the Cannery seeking to recruit employees in just that capacity.
Other than being able to play rudimentary poker and being fluent in the English language, the duties of a Cannery proposition player are as follows:
1. Safeguard the assets of the company. 2. Be responsible to the Poker Floor Supervisor. 3. Must play in games when directed by the Floor Supervisor. 4. Must relinquish his/her seat when directed by the Floor Supervisor. 5. Be familiar with playing protocol of all games spread in the Poker Room. 6. Maintain a bankroll sufficient to last a 6-hour shift.
Our favorite "physical requirement" is this one: "The ability to retain his/her composure and professional demeanor in times of unfortunate poker-hand outcomes." That’s right – you’ve got to have a (literal) poker face.
One other place we've seen full-time true proposition players is in California, where they might earn up to $25-$30 an hour, sometimes with benefits and maybe even a free meal per shift. Prop players in California are normally required to have a gambling stake on deposit at the cashier's cage of the host casino, often to the tune of $10,000-$20,000. They don't always have to play higher-limit games -- many won't play above the $4-$8 level - but those who are willing to play higher-limit games get paid a larger hourly rate.
Being a proposition player has its unique set of challenges. For one thing, you're often playing in short-handed games. If a table is full, the poker room doesn't need a prop there, so you're put in games with fewer players. Short-handed games require a different strategy than full games and can often result in bigger swings in your bankroll. A prop player needs to have a solid short-handed game.
Another drawback to being a prop is that you don't get to choose your table. Poker pros look for tables with inexperienced and weak players. As a prop, you play where you're told, even if they put you in a game with Doyle Brunson and Johnny Chan. You can also find that you get moved around a lot: You get put in one game, then it fills, so you’re pulled from that game and put in another one, and so on.
The rare proposition player excepted, you will see sometimes in Las Vegas one of the floor supervisors sitting in the game to try to keep it going. They normally use their own money, playing passively and seldom raising other players. (Raising is seen as aggressive and doesn’t endear you to your customers.) On the other hand, some floorpeople like to get in the game and "mix it up" when they play. You'll be able to figure out which is which pretty quickly.
In Vegas, you may also see dealers play in games to keep them going. Sometimes they'll clock out to play; other times, they'll play when they're on break, but still on the clock. They’ll deal when it's their turn sometimes even in the same game they're playing! (They leave their chips at their playing position for the half-hour or so that they're dealing.). Note that while passive play is typical of floor supervisors in a game, this is rarely the case for dealers. Often dealers play aggressively and even anger the same players they're expecting tips from when they're working.
Some dealers can be very good players. Scott Fischman and Joe Awada, two World Series of Poker bracelet winners, come from a background of dealing poker in Las Vegas, for example.
Many poker rooms have a sign on the wall that states they reserve the right to employ shills and/or proposition players. In Nevada and in California (and we assume in other jurisdictions), if you ask the poker room if there are props or shills playing, they’re required to identify them to you. They're not required to identify them up front, but if you ask, by law they must tell you who they are. That's the easiest way to tell if any are playing in your game.