I notice a lot of forums in particular have arcades. I must admit I've become hooked on a few online games in my time.

I assume that it's good to have people going to a site for any reason initially. Is there another benefit of arcades - Does Google take them into consideration either favorably or not?

Arcades benefit the creator of the games. Often, these games have links to the site of the game creators, and that counts as a backlink.

In terms of your own site, unless you allow your games to be featured on other sites, you will not benefit in terms of SEO for offering games on your site.

However, if your site has a gamer audience, and the games are up to a certain standard, it might benefit your site in terms of visitor retention and insuring gamers keep returning to your site.

one place i visit regularly has a massive arcade, but to play it you have to first make three posts...

That is each day you wanna play, you have to make the three posts first... Generates posts and increases traffic. There is a competitive edge so people keep coming back to play and beat each others scores.

The arcades can be a lure. I know, too, that some sites create a reason to play. You get some bonus or prize for playing, creating a win-win-win scenario.

I have been pulled into the online gaming thing for a while because of one reason that many of my friends are also playing the same games....but I do not think I would be especially going to a site for their arcades...

Arcades are not necessarily gambling. The sites I frequent that have them are just games and not what I consider gambling. Of course, I don't do them anyway.