I just went through this recently (last week as a matter of fact). Luckily, I have been backing up my PLSQL Dev settings for some time. On my previous WinXP machine, the following was a part of my regular backup script:
echo ###Backing up PLSQL Developer files
regedit.exe /e "\\server\data\Users\<username>\PLSQLDev_Backup\RegistryBackup.reg" "HKEY_CURRENT_USER\Software\Allround Automations\PL/SQL Developer"
%backupcmd% "%ProgramFiles%\PLSQL Developer\Preferences\<username>" "%drive%\PLSQLDev_Backup"
%backupcmd% is defined as: xcopy /s /c /d /e /h /i /r /y /k
On my Win7 machine, the files backed up in the Program Files directory have a new location. I had to restore them to:
C:\Users\<username>\AppData\Roaming\PLSQL Developer\Preferences\<username>
Then I had to run the registry backup on my new computer.
This brought over all my connections, toolbar customizations, settings, everything.