I found the newsletter where Martin Thorborg write about the issue with "Registering to buy something"
Martin Thorborgs Nyhedsbrev nr. 15
It is in Danish, but I will give you the numbers of sales he reckons you will lose:
He estimate that a shop will lose 50% of their sales because of this!
He help a website called
Velkommen til Oestrogen.dk - Danmarks største portal for kvinder. - Oestrogen.dk which is made by a TV talk host called Pernille Aalund. He made some changes to her site and over the next 6 month sales had gone up around four times. He believe that the main reason for this huge rise in sales was the removal of "Registering to buy something" feature
A little background on Martin:
He founded one of the first independent ISP's in Denmark in 1995
They get a lot of call from customer who can not remember the names of websites they have visit and ask for it – He has described it as Google over the phone
They therefore create
Jubii - Forsiden portal and later search engine, Jubii is later sold to Lycos.
He have been involved as an consultant in several websites and have written in articles in large amount of the press in Denmark.
His latest creation
Spam Filter for Outlook and Express, Windows Mail and Servers - SPAMfighter has just won the prize the yearly prize for growth from IT magazine
Computerworld - Computerworld
On top of that the have founded the largest forum for entrepreneurs in Denmark
Iværksætter Debatten Amino and is one of the first people to be called when journalist have a question about the internet and shopping.
Here is what he say about himself in English:
Martin Thorborgs homepage about his life and peptalks
I think that a loss of 50% of potential customer sounds quite high, but I can only guess on what it is as I have not experience on the subject other than what I read. On the Danish forum Amino other web shops have mention that it has increased sales after they remove the feature, as I mention before I think some of them said they saw an increase of 5-6%. I have not been able to find the post where it was mention.
But it would be interesting to hear what happens with
DeadGoodUndies - Mens Designer Underwear, Mens Underwear, if you do any changes to your site.