As a long-time user of Resco Keyboard Pro (I bought it in July 2004!), I downloaded the new version as soon as it became available, so I figured since I was trying it anyway, I might as well chip in with my thoughts here!
As far as I can see, there has not been much done with the 'classic' skin layouts from the previous version (although it does seem a bit snappier when changing between layouts e.g. abc<->123), and the biggest change is the introduction of the 'thumb-able' iSkin layout.
This works extremely well, and I found I was able to type short messages quite quickly and accurately. The downside, as other people have pointed out, is that the SIP is very tall and covers a lot of the screen. This is not such a problem in applications where the screen will scroll (like notes or messaging), but in applications where the screen layout assumes a SIP of standard height (yes it's naughty, but there are plenty of them), it soon becomes unusable. Plus, in landscape mode, it's really only usable for typing notes or messages, as only a couple of lines remain visible at the top of the screen - inputting data into an application or dialog is out of the question. To be honest, I am not sure of the need for such tall, thin buttons on this skin; I suppose it gives a little more tolerance for inaccurate finger placement in a vertical direction, but the left/right tolerance remains the same, so I can't see that much is gained. I would like to see this skin implemented with (at least an option for) a version that is not so tall - I think that would make it a lot more usable.
The other issue I have is the question of switching skins. What I really want is to have a thumb-able keyboard set as default (so that I can quickly send or reply to an email or text message), but to *easily* be able to switch to a standard keyboard if I want to enter an appointment in PI or do something else that really requires stylus input. It is simply too fiddly and time-consuming to go into the input method options, or to select another input method from the list. I have not yet seen this easy switching capability in any keyboard, including this one. The first keyboard that I see with this capability will get my $.
This sounds a bit negative; actually the new version is a big step forward for Resco Keyboard Pro, and I will probably upgrade to the latest version (using Resco's 50% discount offer for existing owners) unless I happen to win a free registration via this contest

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Cheers,
Ian