The post is a bit confusing, though, because well before you get to the line that you quoted, the article states:

"And we’re upgrading all Linodes to 8 cores! Right now. As in all you need to do is reboot to double the computing power of your Linode. By the time the host refresh is completed the average Linode will be running on hardware that is less than 1 year old."

I, for one, thought that it was ready now after reading that. In fact, from the comments, it's clear that for some customers, this is in fact ready:

"BizzarTech: Rebooted my 1024 and moar cores!!! Thank you!!"

No, the move to new hardware and increase in the number of available cores is separate. If you reboot right now you'll get access to more of the 'cores' on the host system (though I suspect they're really just "threads" in Intel terminology). But you're still running on the older L5520 hardware.

I rebooted and confirmed; indeed the older L5520 is still the processor being used on my particular linode:

<snip>

    processor       : 7
    vendor_id       : GenuineIntel
    cpu family      : 6
    model           : 26
    model name      : Intel(R) Xeon(R) CPU           L5520  @ 2.27GHz
    stepping        : 5
    microcode       : 0x11
    cpu MHz         : 2266.746
    cache size      : 8192 KB
    physical id     : 0
    siblings        : 8

</snip>

This is from a plan that is less than a week old:

  processor	: 7
  vendor_id	: GenuineIntel
  cpu family	: 6
  model		: 44
  model name	: Intel(R) Xeon(R) CPU           L5630  @ 2.13GHz
  stepping	: 2
  microcode	: 0x15
  cpu MHz		: 2133.460
  cache size	: 12288 KB
  physical id	: 0
  siblings	: 8