Today, iPad users will see a new compose window (pictured, right) when using the Gmail web interface on the Apple iPad.

While Apple (AAPL) is the clear leader in the large touch screen device space, the new functionality of Google’s (GOOG) Gmail will be a worthy addition to all larger touch screen devices, especially those running Google’s own Android OS, which are expected  to debut en masse later this year.

I checked 640×960 pixel iPhone 4 simulator, which doesn’t invoke the new composer.  While there are plenty of pixels to see this kind of functionality on the new iPhone’s Retina Display, they are grouped so close together that the windows and writing would probably be too small to be useful.

Dell’s (DELL) Streak mini-Tablet has the same 800×480 resolution as HTC’s larger smartphones so it wouldn’t be a good candidate for this type of functionality either. However, Samsung has confirmed a much higher resolution tablet for later this year, which will likely see this update.

For now, the update has only hit US English, but like all other things Google, it will gradually make its way across the globe.

Old and new compose features are compared below: