Not just Intel and Windows/Linux, Apple have admitted the same thing. Probably Android too, because the ARM CPU is affected...
The 30% drop in performance is only an estimate, if you only game/internet you won't notice. Only kernel mode switches are affected, so if you
do a lot of network/disk IO you will definitely notice it.
One story going around is that the Intel boss sold stock just before the announcement (they have known about it since June last year).