In terms of execution the development and release of Perl 6 was undeniably a flub. What eventually got released was ultimately a fine language, but it was years late, largely incompatible with existing Perl code (hence the rename) and a sizeable portion of what was left of the Perl community didn't adopt it and stayed on Perl 5.x. Sizeable enough that there are now some rumblings around tidying 5.x up a bit and releasing it as Perl 7.