Where are the phones with four antennas? Ericsson and Telstra used 5 carriers for a gig last year; Deutsche Telkom with Huawei now announced their "field" test with 5 carriers. SK in Korea and Telstra promise the gig in 2016; AT&T in "12-18 months" (Tom Keathley.) No one will be surprised if those schedules slip, or if the first "deployments" are more like field tests. But it's coming.
As far as I know, none of these networks are actually delivering more than 400 megabits peak today. Since 2009, LTE has been planned for 100 MHz of spectrum, 8 antennas at both transmitter and receiver, and other improvements to reach far beyond the gigabit.
Your speed will vary. The cell edge will be 90% slower; some windows and walls can be equally devastating.