I have been using Backtrack for 2 years and I have heard no news of any spyware or 'phoning home'.
Also, have you seen the photos of the NSA using Backtrack?
Metasploit and w3af actively work with the curators of Backtrack, which shows some level of confidence in the distribution.
Also, with the number of people running packet sniffers attached to Backtrack as part of their penetration testing, any anomaly would show up immediately.
Because everything in Backtrack is open source, every package added to the distribution is verified before release. You can even check things out yourself.
Does this help?