Mozilla released Thunderbird 2.0.0.19 today.  The release notes are here.  This release addresses a number of security issues, most of which were also in the Firefox browser fixes 3.0.5 and 2.0.0.19/2.0.0.20 earlier this month.

  MFSA 2008-60 - Crashes with evidence of memory corruption (rv:1.9.0.5/1.8.1.19)
  MFSA 2008-61 Information stealing via loadBindingDocument
  MFSA 2008-64 XMLHttpRequest 302 response disclosure
  MFSA 2008-65 Cross-domain data theft via script redirect error message|
  MFSA 2008-66 Errors parsing URLs with leading whitespace and control characters
  MFSA 2008-67 Escaped null characters ignored by CSS parser
  MFSA 2008-68 XSS and JavaScript privilege escalation