For a while I have been playing poker for fun, but I am now interested in playing some games at the casino. I would like to observe some games before I start playing. Will it be ok for me to do this?
I did this at a local casino, back in the days when I haunted it. As long as you stand back and don’t kibitz or bother anyone it should be fine.
You can watch… You can even sit at the table as long as you’re with someone playing…
Edit: I’ve never gone up to a game alone to sit and observe, so I’m not sure of the issue there. Although, if you’ve been playing, and lost/won a few, there’s really no limit to your break…
In both cases just be ready to give up your seat if a player comes. That’s all that is requested.
As others have said, it’s allowed.
If you feel a bit nervous about it, feel free to talk to the pit boss in the poker room, and ask them where you can stand or sit to just watch. I guarantee that here in Las Vegas, most will actually help you find a place to watch from, and ask you if you have any questions about the game.
Casinos don’t make much money when they alienate potential gamblers/clients/guests, so most are happy to help out someone who is new to casino gambling etiquette.
In Atlantic City, there is no problem at all with people watching. My sister used to ride down with my friends and I during the summer and watch us play poker. If there was a seat free then they would let her sit but she would mostly just stand back and behind us. There was never an issue from anyone at any of the casinos and she knew us. Like Snowboarder Bo said, just talk to the pit boss and ask where it is okay for you to stand.
I have personally watched high stakes games and it is very informative. Enjoy!
I haven’t played at a casino, just, um, other locations. But you raise a key point people should pay attention to – stand back! There is little I hate more than somebody watching me play and being right behind me, crowding me.
One time, I even had a guy say out loud, “How could you fold that?!” (Obviously, he was so close he could actually see me look at my cards!) I about punched him.
Most poker rooms have a rail running along the outside. Many casinos put no limit tables right next to the rail, as they tend to be exciting to watch. Lean on the rail, don’t say anything about the play and enjoy!
Just a warning, lots of times high stakes players DON’T want to be rail birded, so I wouldn’t try to get too deep into the room to watch.
A rail bird is just a stranger leaning on a rail watching a game. “Sweating” a player typically means you are invited by a player to sit behind them and watch. Big games often have people sweating, but they are invited, not random strangers.
Whenever I play live, I’ll get on the list for a game and then go up and down the rail, watching the games, looking for good action. This is completely acceptable and you will never be chastised for watching as long you are polite and quiet.
As others have said, you can usually watch. Personally, I’d recommend just sitting at a low stakes table and playing really tight for a few rounds. You’ll get the hang of it much faster than by just watching, at the cost of a couple rounds of blinds. Then just start raising every hand – no one will know what to do with you at that point.
'Til they get a good hand and re-raise you or slow-play you and take your stack, of course. 
Also…try not to peak at peoples’ hole cards. Even if you don’t give anything away many are extremely superstitious. Poker player Eric Seidel was chastised for hiding his hole cards from the cameras when they were first installed at the top events. And it’s fun to try to put people on hands anyway.
This is why I only play limit.
As others have said you can certainly watch from the rail at casinos. But I would also suggest watching games online at any of the internet poker rooms. You can see hundreds of hands per hour instead of the 10 or 20 hands per hour you might see in a live game, and you always have a clear view of all visible cards without breathing down anyone’s neck. You can even watch several tables at one time. A lot of online poker rooms have famous pros playing too, so you can watch the likes of Chris Ferguson, Phil Ivey, Doyle Brunson, and many others playing online almost daily. You can sit right at a $10,000/$20,000 limit game between 2 pros (or one pro and a foolish rich guy) and watch every play they make without intruding on their space. At stakes like that very few casinos will allow railbirds unless it is a big event like a publicized tournament.
Surveillance and Security take an extra long look at someone who doesn’t appear to have any intent to gamble, who is watching other gamblers.
Things they look for are people who are alone and not gambling, looking at other gamblers. If you fit all the criteria of a guy who might be looking for a target to scam or steal from or mug, be prepared to show your ID to a security officer and explain what you’re up to. If you give a creepy or hesitant or frightened vibe, it’s entirely within Security’s power to decide they’d rather not risk having you around, and ask you to leave.
On the other hand, if you speak with a poker manager or pit boss or “casino host” (the job title of people who’s only purpose is to get you comfortable enough with a casino to lose all your money there) you can avoid all the trouble about looking suspicious. It also helps if you look like you’re having fun, so wipe the scowl off your face and don’t glance nervously over your shoulder or anything. 
I’ve only played limit a few times, but found it a bit dull. Plus, I don’t like that you can’t force a player to make a decision that involves more than math – to the point that they are forced to call because the math says they should, and then they suck out on you. If I have a hand, I generally want to force them to make a decision that could cause them to make a mistake.