Same here - on the Beta channel, Max OS X 10.10 (Yosemite), Opera Beta 25.0.1614.35. Crashing every few minutes regardless of activity. Running the latest release of Flash (15.0.0.189). Crashlogs are identical to squ1b3r and dmitrden:
Crashed Thread: 0 CrBrowserMain Dispatch queue: com.apple.main-thread
Exception Type: EXC_BAD_ACCESS (SIGSEGV)
Exception Codes: EXC_I386_GPFLT
This install was stable under Mavericks.