In iOS 4.0 Apple has redesigned the backup process.
iTunes used to store a list of filenames associated with backup files in the Manifest.plist file, but in iOS 4.
For those looking for a Java implementation of a MBDB file reader, there are several out there:
"iPhone Analyzer" project (very clean code): http://sourceforge.net/p/iphoneanalyzer/code/HEAD/tree/trunk/library/src/main/java/com/crypticbit/ipa/io/parser/manifest/Mbdb.java
"iPhone Stalker" project: https://code.google.com/p/iphonestalker/source/browse/trunk/src/iphonestalker/util/io/MBDBReader.java