I'm sure there are plenty of threads about a Western rider switching over to dressage, so I'll browse those in a bit.
By way of quick background, I've owned/worked with/trained horses for over 20 years. I've ridden Western (mostly just trail and pleasure riding) my whole life, although I have ridden on an English saddle and an endurance saddle on my Arab (in the search for a saddle that would fit him best). The thing that struck me most about riding in an English saddle was how much more "in tune" I felt with the horse.
Ideally I'll take some lessons, etc. in dressage before investing in a dressage horse for me, but I happened to stumble across this mare and was wondering what some of the experienced dressage people thought of her:
StormyRide - YouTube
StormyRide2 - YouTube
She's apparently done some 2nd level showing. She's an 11 year old Anglo-Arab.