From:runescape.com

We would like to remind you about the removal of unbalanced trade, which will happen on the 2nd of January, 2008. Please prepare yourself for this change as you will not be able to make unbalanced trades once the date has passed.

We will be introducing a change on the same day, which will allow you more flexibility when trading. As you may have read in our Future Changes to Recent Updates newspost, this is an increase to the 3,000gp staking/trading limit, based on the number of Quest Points you have.

More details will be given in the Behind the Scenes newspost, and on the day of release.