Just got QGIS 2.6.0 running on Windows 7 service pack 1 64 bit. Project loads, edits, saves editing changes, adds removes, layers no problem. Only problem is saving the project. Do that and it's certain death. You get a mini dump crash error.
Then you attempt to open the project again and it says unexpected end of file at line'x' and shows the file as being 0 KB. Restore the project to a previous version and it happens again EVERY TIME. This also happened when I upgraded to 2.4. What gives? Yes, going to be writing a bug ticket also.