Please note:

• You need a working Internet connection on the machine running LINQPad when you enter your activation code (what if I have an isolated network?)
• LINQPad sends some hardware information to the licensing server during activation
• Only C# 5.0 / C# 4.0 / C# 3.0 is supported (not Visual Basic or SQL or F#)
• You may be sent a replacement activation code periodically
• Your license is good for updates to LINQPad 2.x (for Framework 3.5) and LINQPad 4.x (for Framework 4.0 and Framework 4.5).