I have BigDecimal objects serialized with BlazeDS to Actionscript. Once they hit Actionscript as Number objects, they have values like:
140475.32
turns
GraniteDS 2.2 has BigDecimal, BigInteger and Long implementations in ActionScript3, serialization options between Java / Flex for these types, and even code generation tools options in order to generate AS3 big numbers variables for the corresponding Java ones.
See more here: http://www.graniteds.org/confluence/display/DOC22/2.+Big+Number+Implementations.