There are some good points here

I work in a Pharmacy with an open plan dispensary - it can be both a blessing and a curse:
When you are doing a person's prescription in an open plan dispensary it can actually open up opportunities for counselling and patient queries and like Jeff (i think) said helps you to be involved with the patient personally and get to know them and allows you to notice the times when they are feeling a little 'down in the dumps' or not themselves. Even if its only chatting to them about the footy, it strikes up a rappor (is that the word i'm looking for) and makes patients come back to you - I know we have regulars who miss our chatty Pharmacist when he's off.
However, on the flipside, I think open plan dispensaries can contribute to errors as you have patients staring at you and eye balling you, huffing and puffing that they are not being served as fast as they would like and the bench gets covered in scripts and it looks downright untidy!
(but then thats just my tuppenorth worth

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