...and if you believe that, I've got a bridge for sale. Titanium is many things but soft it is not. It can also be alloyed with many other metals for specific purposes. One thing it definitely is though is expensive which is most likely the reason for Apple to look for alternatives. That is actually is possible to use titanium to create form-stable notebooks can be seen by e.g. the many Thinkpads which sport titanium lids and frames. I have yet to see one of these warped or bent. This is partly due to the boxy - and with that, strong - form factor but the material plays a big role as well.
The T-series (at least from T2x to T6x) had titanium lids. I don't know what they use nowadays as I am in the habit of using older machines (currently using a T42p with 1600x1200 4:3 screen). The T21 I'm using as a mobile terminal to access headless servers has been used as a seat cushion more than once, the screen hasn't budged...
Titanium is also a relatively poor conductor of heat. Aluminum conducts heat over 10 times better than Titanium. Use of aluminium would be much better at conducting heat away from the body of the notebook.
