Object Pooling in Java

What are the pro's and con's of maintaining a pool of frequently used objects and grab one from the pool instead of creating a new one. Something like string interning except that it will be possible for all class objects.

For example it can be considered to be good since it saves gc time and object creation time. On the other hand it can be a synchronization bottleneck if used from multiple threads, demands explicit deallocation and introduces possibility of memory leaks. By tying up memory that could be reclaimed, it places additional pressure on the garbage collector.