This is what happens when a book view is executed in EDS:

[get vCard from database]
contact = e_contact_new_from_vcard(vcard)
e_book_view_notify_update (contact)
vcard = e_contact_to_string_vcard30
[now send string over IPC]

Looks harmless, but if you profile this 68% of the execution time is spend
measuring strings, 99.9% of the calls coming from e_contact_to_string_vcard30.

This is basically because e_data_book_view_notify_update() takes a EContact, but
the database has just retrieved a vCard and the book view needs to send a vCard
over the wire.

Attached is a prototype patch to e-data-book-view.[ch] and
e-book-backend-file.c, which has a non-negligable effect on performance (test
creates 300 book views).

Before:
real    0m12.179s
user    0m1.741s
sys     0m0.046s

After:
real    0m3.737s
user    0m1.740s
sys     0m0.052s

Now, this is a prototype patch as this is probably going to be a right pain for
some backends to support, where vCards are not the native transport format. 
Maybe e-data-book-view needs notify_update(EContact*) and notify_update(char*)?