1. Underscore looks ugly. We need better approach to represent class
attributes.
2. The variable name with type info sounds like hungarian notation[1]
to me.  It may lead to inconsistency when code is changed. Its good if
you know the type of variable, but
    what if a programmer does not know the purpose of such variable ?
For at least interface class, we can use such convention.
3. I disagree allowing _ in filename. The filename should be same as
classname or common functionality name without _. lke
   Class ZendLogAdapterInterface
   As you know Zend is following exact underscore convention [2] but I
still prefer using Java style.
4. How constant should be declared. Its missing from the convention.
5. Coding Style is very important. I recommend using the Zend Coding
Style:  
http://framework.zend.com/manual/en/coding-standard.coding-style.html
PHP has became a kitchen sink of features grabbed from Java,
especially in OOP paradigm.  We need to look in the Java coding
conventions and follow
the same if necessary.  Guys, share you opinion.
--
Sarose
[1] About Hungarian Notation [ 
http://en.wikipedia.org/wiki/Hungarian_notation
]
[2] Zend Coding Convention  [ 
http://framework.zend.com/manual/en/coding-standard.naming-conventions.html
]