Depends. If you treat it as (relatively) cheap entertainment that sometimes lets you leave with more money than you started with, and play with disposable income, it's no worse than a lot of other things. And you get free drinks!
If you're expecting to make money consistently, you have a few choices:
1) Find video poker machines with >100% payback (they're rare these days, but can be found.) Play them perfectly. Variance is very high (most of the EV comes from quads and royal flushes, which you can go thousands of hands without hitting), but you will make money over time. Comps can help.
2) Count cards at blackjack, preferably single-deck with favorable rules. The variance is still very high (Stanford Wong's 'Professional Blackjack' gives estimates like $25 +-$400 per hour for +EV play and making $25-$100 bets), but you can make money over time. However, if you get really good and play a lot, the casinos may bar you or do things to make your play difficult (like shuffling every few hands).
3) Play poker. Since you're not playing against the house, you can actually win consistently. Although beating the rake at low limits is really really hard, and you need a sizable bankroll to play higher-limit games (and, of course, you'll be up against much tougher competition in the high-limit games, so you'll need to be very good to win consistently.)