Not leaving (yet), but watching my options, which is why I paid full price for my GS2 in October in order to have flexibility to re-up or jump in June when I'm out of contract. If anything, I may just go month to month if I can keep buying phones for five bills and not get chained down.
In Detroit, they never really got 4G up outside of the Wayne State/New Center areas and even there is was sketchy and unofficial. Last weekend I was in downtown Royal Oak and my speeds were breathtakingly fast. I drove a mile away, went into a diner and sat by the window and had 1 bar, if that. Bars have no relation to data speeds and I'm getting tired of my girlfriend staring at me while I wait a minute for a page to load before she says, "I thought that phone was supposed to be fast."
OTOH, Verizon are pure evil, so our choices are fast, expensive and evil or not too evil and a bargain, but craptastic data speeds.