0.20, compared to previous versions, doesn't let you save with a timestamp in the future and will set it to current time without telling you. This is really bad for users upgrading to 0.20 that were using those timestamps.
hbase(main):004:0> put 'testtable', 'r1', 'f1:c1', 'val', 5373965335336911168
0 row(s) in 0.0070 seconds
hbase(main):005:0> scan 'testtable'
r1 column=f1:c1, timestamp=1251223892010, value=val
1 row(s) in 0.0380 seconds