Yes, I've found that undestanding & visualising/being mindful of the layout helped a lot, especially at first, to unlearn QWERTY memory & learn the DVORAK layout. Practising on paper is a good idea, and also a quick & easy way to try out the ease of typing on a DVORAK layout - one should notice the smoother & easier typing motion straightaway
.
I know what you mean about the vowels' key order: some of the other positions seem a little odd too, like S on the extreme right when its more common than D or H for instance, but like you say there's probably a reason: its said some common key combinations are also supposedly optimized e.g. TH, SH, NT, NG, _D, _H, _T etc. are all layed out such that they are typed in an "inward" direction towards the centre of the keyboard, so that the fingers type in an order from the "outer" e.g. fourth, little fingers, towards the inner e.g. index finger, which is supposed to be more ergonomic
. At least all the vowels are grouped together, anyway!
P.S. just added
this link to my initial post, as a useful source of more information on DVORAK.
Stuart.