I was never really sold on the SD card. It must have a following elsewhere in the world. If you're going to splurge at some point I'd sit tight for a BeoSound 5. Better to get something that can play all of your digital music and not just what fits on an SD card. 

I have a Beosound 4 -  I purchased it for the SD card compatability with my Beosound 2 and also for DAB.

As things turned out:

• the SD card has been used to record a few radio broadcasts - very few, but very important - for that alone it was probably worthwhile but not something I knew at the time of planning and buying !!
• I tend to leave just one high capacity SD in that contains a selection of my wife's favourite music that we use as background to dinner parties
• I am always amazed at how rich the sound of the music from the SD is - it seems as good as the original CD
• the DAB has proven to be a non-event - we no longer listen to any radio except in the car

However these things irritate me about the design:

• inserting CDs is cumbersome - I always fear I am going to scratch the CD
• when the glass door closes there is a click as the door catches the outside edge of the CD (but doesn't while the CD spins - go figure)

I hardly use the Beosound 4 these days, but I will keep it - and in that role I wish I had a Beosound 3000 or overture as I think they are more beautiful works of art/design

When the B&O future landscape stabilises I will buy a Beosound 5/Encore ... but not as a replacement of my Beosound 4 - my wife is wedded to CDs even though she does like the tactile nature of the Beosound 5/Encore