Andy Manson (the luthier responsible for The Mermaid and John Paul Jones' triple neck acoustic among others) reckons that a cut away makes no difference to the overall sound of the instrument.
The Manson guitar used by Julie Ellison as her main gigging instrument features a very curvy cut away combined with different body/neck position and - most importantly - no heel, a feature specifically requested by Julie to avoid the fretting problems mentioned by Grab. All frets are easily accessible and sound as crisp and clear as any postion on the neck.
That said, Andy Manson's guitars are pretty special!
This feature is available on many other guitars made by Andy. Although he doesn't make "models" as such - all his guitars are individual - features often pop up in different guitars.
You can see a photo of Julie's latest Manson at http://www.andymanson.co.uk/ellison.htm and http://www.julieellison.co.uk/promo.shtml#photographs
(page down to the third photo)