We're using ehchache 1.6.0 at the moment. This is now 2 year old. Also later versions have a smaller memory footprint:
"Update: Ehcache 2.0 will introduce a new implementation for MemoryStore based on a custom ConcurrentHashMap. This version provides fast iteration and does away with the need for the keyArray thus bringing memory use back down to pre 1.6 levels. And with other memory optimisations made to Element in 1.7, memory use will actually be considerably lower than pre 1.6 levels."