For the pound cake: Slice the pound cake into 2-inch thick pieces and set aside.
For the guava cream: Place the guavas, condensed milk, cream cheese and lime juice in a blender. Process mixture until smooth. Strain the mixture into a bowl. Discard the seeds. Set aside.
For the guava compote: Bring the guavas, 1 cup water, the sugars, butter, cinnamon and vanilla to a boil in a heavy medium saucepan. Reduce the heat to medium low; simmer until almost all the liquid evaporates, stirring often, about 30 minutes. Cover and chill. (Can be made 2 days ahead). Serve warm or at room temperature.
To assemble the pound cake: Place a slice of pound cake onto a serving plate. Drizzle with the guava cream. Top with a spoonful of guava compote. Garnish with 4 blackberries. Dust with some powdered sugar and serve.