I got a d500 after my mate did and it is fantastic!
I upgraded from an e700 by the way, which is the predecessor of the e720.
The only thing I can think of at the mo which my sister mentioned is that unlike her Nokia, you can't listen to MP3s in the background (i.e, while writing a text or using wap) I assume this is the same for the e720 though as the software will be very similar.
However, when I'm listening to my MP3s, personally I'm not really going to be multi-tasking anyway. It'll probably be when I'm sitting on a bus or train and just something to fill the time and keep me entertained so that causes me no problems and bothers me not.
The 80mb of storage is very generous and the videos and pictures (even the excellent quality megapixel ones) take up very little space. Hardly any compared with how much you're given to use up.
I still havent managed to fill it up and thats something, considering how much crap I record on it.
The picture quality is amazing. By far the best of any other camera I personally have seen on the market. I don't claim to be an expert or anything but I did do research before I bought it and compared it with samples of photos from other phones.
Lovely little phone and I'd definitely recommend it.
Out of the two though, I dunno. I don't know about the other one but I'm guessing it's quite the same.
If you go to the Carphone Warehouse or some place, I'm sure they'll let you have a little try of both phones.
Just don't let them pressure you into buying something completely different or something you don't want.
Good luck!