I too use my Evo almost constantly, but considering that I get on wifi whenever I'm able to, I have a very hard time reaching even 1gb.
I started with a 3gb data plan for $35 with my Verizon Tab; I've been using it hard since I bought it two weeks ago. However, to this day I've managed to use all of 90mb (MB!) of 3g data, so I just called Verizon to downgrade to the 1gb plan for $20. I just couldn't justify throwing $15 away every month for 2 additional gb of data I was never going to use.