The iPad was released over 5 months ago, on April 3, 2010, and we’ve yet to see some of the biggest iPhone apps be updated to take full advantage of the iPad.

The biggest Twitter app was Tweetie, which then turned into Twitter and has a ton of fans. However, it’s still absent on the iPad.

While we await Twitter, Twitterrific is quickly raking in the money as its by far the best Twitter app on the iPad. Its price tag of $4.99 may be a bit much for some, but it beats waiting for Twitter to release their version.

Then there is Facebook. Isn’t Facebook the biggest social network? And yet they don’t have an iPad app either. Granted, the web version works just fine, but the push notifications, optimized layout and an all around better designed iPad app would be much nicer.

What about FourSquare? Everyone is on FourSquare and it’s growing quite fast. And yet, there is no iPad app. I guess, it takes only seconds to make a check-in, so using the iPhone version isn’t terrible, but an iPad version would be ideal.

Possibly the biggest iPhone game ever has yet to be updated too. Doodle Jump took the iPhone by storm and sold millions of copies. So why hasn’t that been updated to take advantage of the additional screen real estate? Heck, for 99 cents, I’d buy the exact same game if it were just optimized for the iPad.

Maybe not one of the biggest apps, but one of my favorites is I Can Haz Cheezeburger and I’d love to see updated so I could see the LOLs in higher quality.

Granted, all the apps above do work on the iPad, they just aren’t optimized for the iPad. And, unless you like pixley, fuzzy or small images, you’re probably eagerly awaiting updates too.

There are lots of great iPad apps out there, but it does surprise me that, after 5 months, some of the most successful iPhone apps have yet to create iPad versions.

What’s the hold up?