I live out in the boonies, so I can't get a regular high speed internet connection (DSL, etc.).  What I can get is satellite internet.
 
The problem here though, is the time it takes for the signal to go from my house, up to the satellite, to the ISP, back to the satellite, and down to my computer.  This time is roughly 1 second!
 
So, half that time would be a 500ms ping, right?  Thats really bad, isn't it?
 
My question is, could I still do some online gaming (like WOW, or Guild wars) with this kind of latency.
 
Or put it another way, would you want to play a game with someone with that much lag?  I know games tend to minimize reaction time for this, but still 500ms is a lot.
 
What say you, yea or nay?

I have known a couple people who have played WoW but they couldn't use vent along with it.  Thats also about the same ping my friends get on the US servers when they are in Australia.

Technically, your ping is a two-way measurement; it includes the full to-the-ISP-and-back loop.
 
As for those games, 500ms, if that's your ping, will be fine; 1 second would be tolerable; PvP will be markedly harder than PvM with a higher latency. Most MMOs don't require good reflexes. Ultima Online would be a different story, though.

It does depend on what kind of game you are going to want to play to be honest. Personally I prefer to play FPS' which obviously require quick reactions and I find in those games anything over 100ms can be severely detrimental.
WOW still has a live action element to to, though it's not quite as intense as an FPS so I'm guessing you could get away with upto 200-250ms ping (I've not spent much time playing this so it's only an estimate btw). I must state though even if it's playable it could get frustrating.
Going further up the scale, turn based strategy or slow paced RTS' could probably stand up to even higher pings. I've dabbled in the DEFCON demo (fairly slow RTS) and I've battled through some pretty steep ping times (~400ms) and still enjoyed the game.
Since there are plenty of cheaper, older games with online capability from all kinds of genres I'd suggest actually buying a game and using it as a benchmark for your connection - it'd be worth a try.
 
Good luck!

if your playing supcom, even GPG says you can easily play with 500 ping....

Wow, ok altough you probably will feel lag hurts in PvP where fast reaction helps a lot
 
FPS like Counterstrike, just don't play them above 150ms, a lot of servers autokick you above 100 or 150, the good ones any ways

As someone who still occasionally plays on dialup, some insight.  A great deal depends on the type, and play style you take.  Lets take Diablo 2 for an example, as it's WOW like, and something you can try without an account.
 
A close combat barbarian is a poor choice, because you're going to face the latency every click.
 
A sorceress with blizzard is a better choice.  You still have the latency of the initial click, but afterwards, the spell goes automatically.
 
For a summons druid, or a necromancer with lots of critters, the critters are server side, and not affected by your latency.
 
You're going to have to lead targets more, and recognize situations a full second before they happen, but it's quite possible.
 

For WoW, 500ms is fine (except PvP perhaps).  It is what I am having from where I am from.  Anything beyond can be quite bad depending on how many people are there in the group.  
 
I think the most important thing is consistency.  If your latency is consistant at around the 500ms region, it is much better than having a variation of 500ms to 2,000ms (I had that before I changed my ISP).