There are a few features we don't get in our 3-series BMWs in the States, well at least we don't get them stock. Of course you probably are used to the game of being able to buy OEM parts after your purchase, even if they are parts that could've come on your car from the factory like they are made available across the Atlantic. After owning several BMWs, this has become old hat in my experience.
I fell for it again and decided to order a $265 part (price included shipping) from Tischer BMW, the OEM BMW E90 Sedan Split Armrest (the E90 part fits the E92/E93.) I had put this modification off because it seemed kind of dumb to me, but a couple of good friends did the install and really liked the improvement of the upgrade.
There is also a lot of talk on the boards in a DIY thread concerning the hassle of a small gear you have to install to get the full effect of the upgrade (gives a more natural not so springy pop of the armrest when it is released. Stock just shoots right up.) Anyway the gear was a bit of hassle but two posts really helped: Putting in the spring and the other tip is "So here's a tip so this doesn't happen to anyone else. Once the gear is inserted properly and you're attempting to place the armrest in, HOLD the gear in place firmly with your finger. Trust me, you'll avoid a lot of aggravation."
Another helpful post, involved how to remove the armrest from an E92/E93 as opposed to the E90 model the DIY was originally done for.
Also, before installing the new armrest you'll want to remove your iPod holder from the stock armrest and install it on the new armrest. Details can be found on this post. I removed the iPod holder and used a small piece of card paper for a magazine subscription and made a template from that for drilling the new holes. Be careful not to drill too far in. Don't worry if it pokes right through quickly, as there is just a thin piece of plastic to drill through. Make sure your drill bit isn't long so you continue to the other side, tough to do but just be careful and don't worry when the drill pokes through the thin layer of plastic since you did not go through any leather.
The install took me about 20 minutes including the time to remove and reattach the iPod leather holder.