Your going to find some very emotional posts about this subject. so below is how I have done with the 250Mb plan, and is not indicative of what everyone experiences.
at 250Mb you can use about 8Mb per day and still be under in 30 days time. with the 2Gb plan you have about 66Mb/day.
If your doing less than 4 of your photos a day and sending some text only emails (don't forget, reading emails from others also downloads the pics usually), you should be able to stay under the 8MB a day easy.
I do text only browsing using the Atomic Browser, check email a few times a day and don't do any app downloads if not at home on the wi-fi, nor have notifications turned on (nothing I need to know while at work.) My 250Mb plan still had some space on it 30 days later.
I look at it this way, if you go more than 15 days on 250Mb, its more cost efficient to get the 250Mb plan over the 2Gb plan. If you go 20 Days before having to renew it, at 90 days time, you would have paid out $75US and the 2Gb user would have paid $100US. Almost enough to pay for 40 more days of data. (your ahead of the other user by a full months payment on their plan, in just 3 months).
Just my thoughts and usage, others will swear you aren't using the ipad properly or for what its meant for if you don't need the higher plan. It all depends on what you need.
Jason