I'll be the first to admit that I don't understand the Farmville [Free] phenomenon at all. I've tried several times to get in to the game, and while I've been sucked in to other freemium social time sinks, Farmville just doesn't do it for me. However, this doesn't seem to stop nearly everyone I know on Facebook from constantly offering lost cows, free corn, and all kinds of other junk I can't even begin to understand why I'd want. If you do want those things, and own an iPad, you need to check out the latest Farmville update ASAP.
Here's a before and after of what playing Farmville on the iPad was like, and is like now:
There's also some high definition assets in the game for the Retina Display of the iPhone 4 and 4th generation iPod touch, but on initial inspection this seems to be limited to the splash screen and a few other graphics. Also, if you're super hardcore and have the Super Combine tractor, that's supported in the app now as well.
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