This crash is rather interesting in the fact that we can 100% recreate it when pairing with Thaumcraft by using the Thaumometer and looking at a moar signs sign, however it seems to be able to be recreated on certain hardware from shift+clicking with a sign in either the inventory of the chest being worked with or the users inventory (recreatable about 80% of the time this way). The following is one of the crash reports, all reports given to us so far have had the same trace so I figured the one report should suffice.

http://pastebin.com/sfkwb7ht

I have fixed the issue when crashing with Thaumcraft in 1.0.3, please report if you come across any more bugs.