where is default Bitcoin-Qt data directory? I want to make portable client so I found with start bitcoin-qt.exe -datadir=data

But where is default data dir so I can move it there?
It depends on your operating system.  Read about it here.

Linux

~/.bitcoin/


Mac

~/Library/Application Support/Bitcoin/


Windows

C:\Documents and Settings\YourUserName\Application data\Bitcoin (XP)

C:\Users\YourUserName\Appdata\Roaming\Bitcoin (Vista and 7)