Just because you don't use more than 2gb a month NOW doesn't mean you won't always not use 2gb a month.
There are apps we haven't even imagined yet and haven't even been created yet and with new features, data is going to be at a premium and you're going to really wish you still had that unlimited plan that isn't offered anymore.
Remember the old dial-up days? Imagine if the internet companies offered a tiered plan at 25gb? It might be worth it. I mean, you don't use 25gb a month. Why not save $5 a month? Well, now it's 5 years later and 25gb isn't very much data to have with all the cool things the internet can do now. Now you're forced to pay even more to upgrade to a higher tiered data plan or else you're forced to really cut down on your usage for the last couple weeks of the month.
In the beginning of the world wide web, the internet companies screwed themselves and their ability to maximize profits at the expense of the customers they cater to by always offering unlimited and we the people ended up getting used to it so now if they try to take it away so they can maximize their profits while forcing us not to use their product very much while still charging us the same amout, people will be MAD and won't allow it. The mobile broadband companies are doing their best to not make the same mistake. They want us to be used to having tiered data plans so right now in the infancy of mobile broadband, they're implementing tiered plans and getting rid of unlimited so we're used to having to pay for what we use right off the bat.
I use between 1.5gb and 5gb a month just doing normal everyday stuff with my phone. Streaming music while i exercise, watching YouTube, Netflix, Hulu, etc. Just using my iPhone for what it's meant to be used for. Enjoyment.
Keep your unlimited data plan for as long as you can. In the very near future, 2gb isn't going to last you very long. It may last you now, but when new ideas and innovations to mobile broadband are invented, data is going to be very important.