About 30mb here, but it will probably grow a bit when/if i have to use gps a lot.

I'm on pay-as-you-go with 3 in the UK, they give me 150mb free for each top-up (which is £5 minimum) + free skype traffic, and it's plenty for me -- i have wifi at home and office, so I rarely need GPRS, and I make very few calls outside Skype these days.

I used to be on a vodafone contract, but I never managed to get value for money -- their "£15 per month" always ended up being more like £50...