Which approach do you prefer for implementing long application transactions?

I have used Session-per-request with detached objects extensively, and find it a natural and easy way to work.

However, I notice that Hibernate in Action seems to be in favour of Session-per-conversation (page 329; "we're inclined to think that it isn't [per-request] the best approach for servlet-only-applications")

Unfortunately, as far as I can see, the book doesn't actually explain the reasons why.

Anyone any thoughts on this?

Of course its explained: Because session-per-conversation doesn't require a detached state, doesn't expose you (at least not as easily) to identity scope issues, and does not require manual reattachment.