So here is a new beta:
https://dl.dropboxusercontent.com/u/13064071/plantuml.jar
It supports the following syntax:
@startuml
skinparam note {
BackgroundColor<<st1>> #white
BorderColor<<st1>> #green
FontColor<<st1>> #red
shadowing false
shadowing<<with>> true
shadowing<<without>> false
}
A -> B : msg
note<<st1>> over A : text 1
note over B #line:green;back:lightblue;shadowing:false : text 2
note<<with>> over A : text 3
note<<without>> over A : text 4
@enduml
Is this what you were expecting ?