Blender now is 64 bits safe again. That safety is on two different levels;
Blender's famous "struct DNA", which ensures backwards and even upwards compatibility for files, had to be tested and fixed for full (mixed!) 32 and 64 bits compliancy. Files saved in 32 bits should be readable in 64 bits, and vice versa. Also for appending data and for dynamic linked data (libraries) you should be able to use mixed 32 and 64 files.
Luckily the errors in previously saved 64 bits files were minimal, so those who already were using Blender 64 bits can still read data with this version. Note that it is possible these files will crash with 32 bits, so don't spread this!
All cases in the code where pointers (memory addresses) were converted to integers had to be checked to use 64 bits integers too.
- We had no access to a system with 8 or 16 GB memory for stress testing. It is well possible several issues still are there... please report this to our bug tracker.
- No Windows 64 bits version is available yet. We seek a developer to help with it, especially because we chose the (unix) LP64 standard...
- Only the release of OSX 10.5 will allow us to publish a 64 bits OSX Blender.