I can confirm that both the XML and JSON feeds from SPOT now contain a (new) altitude field. It reports in meters. I have test flown and verified that it is the accurate GPS altitude.

So far, I see this data filled in only in tracking messages. In messages sent in response to a button push, the field appears to be zero.

I also note quite a few instances of drop-outs -- perhaps as many as 20% or 30% of all messages. I speculate that these may be related to instances where the rapid acquisition GPS engine in the SPOT fails to get enough satellites for a 3D solution. In these cases altitude is reported as zero or negative.