The final slide was meant to answer several infamous Valve mysteries -- Who is the G-Man? Why doesn't Valve support the PlayStation 3? -- and perhaps it did in some obfuscated way. According to seasoned ARG sleuths (posting on the Penny Arcade forums), the error code above can be read as: "S U S : P E N D ... U N T ( I ) L ... E E E." Suspend until E3?
It wouldn't be surprising to see Portal 2 at this year's E3 expo, which will run in Los Angeles from June 15 to 17, but if the above decryption is accurate Valve may have additional plans to unfurl (possibly including the long-awaited Half-Life 2: Episode 3).