Well, I can tell you that many thousands of Sony Ericsson phone owners use it because thousands are using Feisar's "Address Book Enabler", which now no longer works with Leopard. 😟
Then there's also all the owners of natively supported phones, plus the users of nova media's Address Book Phone Plugins.
So, I would say that yes, many people did use it.
However, the lack of response is probably more to do with the fact that Leopard's only been out a few hours, not everyone who upgraded will have noticed yet, and not everyone has upgraded anyway.
The particular file that the addressbook enabler patched (ABDeviceCommandSets.plist) is no longer present in the 10.5 Addressbook, all support for devices appears to have been stripped out. Hopefully they can add it back in as I used to use this with my SE W900 pretty frequently.
An alternative which works ok for me is
http://algoritmer.dk/widget/ - Not quite as versatile (doesn't display incoming SMS) but better than nothing. And it's free whereas BluePhone Elite is not.