i get 10to12 mbps on sprints 4g, 10 at day 12 at night.
i would say the difference is huge compared to 3g where i can only about 500kbs day and 2 mbps night.
the reason i need the speed is because i like to watch hd movies and play online games, i use the internet wifi hotspot from my phone as my only internet source at home, so i download games, movies, programs, video chat all kinds of stuff on the several pcs in the home as well as internet ready tvs.
the speed really helps when one person is watching netflix, the other playing xbox live, another wathing youtube and someone chatting on a laptop, you get the idea, alot can be using that line at once as well.