I'm currently using Kubuntu, and sometimes the jobs that run at bootup hang the login screen and even prevent the TTY gettys (i.e. ctrl-alt-f2) from starting at all. In those cases I alt-sysrq-u and reset. Haven't determined whether it's fstrim, unattended-upgrades, a search indexer, or something else, because alt-sysrq-t is disabled in Ubuntu kernels and I can't start a task manager if I can't log in.

It's pretty frustrating, but it's still slightly better than Windows.