When the CRM 2011 Rollup 12 came out, there was a bug around the “Convert Lead” dialog box no longer appearing during the lead qualification process. Microsoft was originally supposed to release a fix for it in a future release and in the meantime, there was a way to get it to work with “old” CRM forms. It was essentially about adding the Currency field to the form (see details here). Since the new UI came out, it seems the Convert Lead dialog box is gone for good.
Going forward, we now have the possibility to select the existing contact and account directly in the lead record. If none of the value is selected, an Account and a Contact gets created. This avoids additional processing prior to the lead qualification and removes the need to have the “Convert Lead” dialog.
This applies to CRM 2011 Online (instances that haven’t been upgraded to CRM 2013 yet) and all CRM 2013 installation types.