There's been a lot of speculation as to the reasons behind TrueCrypt's sudden deprecation by its development team. The main website was redirected to Sourceforge with a vague error message--"WARNING: Using TrueCrypt is not secure as it may contain unfixed security issues"--and without the public mailing list discussion or other early warnings that normally accompany the deprecation of an open source development project.
Silence, however, isn't itself cause for panic. An ongoing audit of TrueCrypt hasn't found anything major, and there is plenty of active interest in evaluating TrueCrypt's current state in the hope of moving it forward. In other words, there's no sign of an existing security problem, and plenty of eyes are looking out for one.
The future of TrueCrypt is yet to be seen.
In the mean time, those wanting to create new TrueCrypt installations should be careful where they get their software. With the TrueCrypt site deprecated, there are plenty copies floating around that nobody's checked for malware or back doors. Ideally, users have the ability to verify a new copy of TrueCrypt by means of digital signature or comparing the checksum against that of a known-good copy. However, absent that, one's safest bet for acquiring TrueCrypt is to use the git archive maintained by the good folks spearheading the ongoing audit linked earlier in this post: https://github.com/DrWhax/truecrypt-archive
Deprecation of open source software projects happens every day. Some get picked up and continued by others, some vanish over time. While the TrueCrypt team's lack of communication with its community may be frustrating, it doesn't change the code, which has not raised red flags. More context may come to light in the long term, but in the mean time even the most cautious among us can afford to take a deep breath.