I think its obvious that the benefits of a 16:10 iPad are highly dependent on your usage cases. All of the examples Piggie posted are content that shines on a widescreen device. Landscape webpages do not look better in the current iOS on a widescreen device.
Above is an example of how a magazine like Garden and Gun would work on the two screen sizes, I used a dark grey background so you could really see what the bars would look like as opposed to black blending with the bezel which might mislead people. Even when I had the larger screen iPad 2 I always read Zinio vertically, one page at a time which would make the bars very apparent. If you like to read your magazines as a spread, 16:10 works better for you. Now G&G is a little more square than say Time magazine, but not enough to change my example noticibly. It's also worth mentioning that comics are a but taller than magazines which means that there would be smaller bars when viewed vertically, but even larger bars when viewed horizontally as a spread.
When it comes to iWork and the like, if it at all needs to be printed the page would still need to be formatted for 4:3, except in the UK where A4 is a little taller. Only legal-page formatted documents would really fill up the taller screen. Now assuming you have a ltr-formatted document on your ipad, it would be centered vertically in the screen and then shift up to display the keyboard, and then move back down when the keyboard is hidden.
Also, if you watch SD formatted videos, like older TV shows, with 16:10 you would end up with black bars on the side as opposed to black bars on top of HD content on a 4:3 screen.
I do still think that if iOS supported split screen dual apps a 16:10 iPad would work better, and I probably would buy one, but not the way iOS currently is. If Apple went with a 1/3 2/3 split they could, for example, allow the iPhone Hulu to run beside the iPad browser. I also think that Retina is required for this to work well, other wise Safari shrunk to fit half the landscape with would be entirely too small; just saying keep the scaling at 100% and cutting the width in half doesn't work because the majority of sites do not reflow all the content so they would look bad.
If Apple releases a 16:10 iPad, hopefully they will do it in addition to the 4:3, as opposed to replacing it like the iPhone, because people view a lot of 4:3 formatted content on the iPad that they don't on the iPhone.
PS: Piggie, I'm not picking on you specifically. Its just that you're the most vocal supporter of 16:10 so I feel like I'm having a conversation with you.