Just a calculation of how many BTC I would get for that asset should I market sell them all right then and there after paying fees.
maybe even put a "cashout" button beside it to execute the market sell (make sure this has a confirmation check)
Save us having to go to the asset page, look at depth, then calculate it all out, etc etc
Most traders use limit orders, but having a market value displayed in the port would with a cashout button may still be a nice feature for some of others.
*edit*
Back when SecondLife was all the rage, I was very involved in the financial community.
A stock exchange (actually a couple) was opened servicing the grid, much like the GLBSE is servicing the bitcoin niche.
Anyhow, long story short, you should go take a look at the surviving exchange: http://www.slcapex.com/
I am sure you will see a lot of good ideas and implementations that could be added to the GLBSE
