SQL allows you to adminster the database directly and allows you to situate it on a remote machine, if you so wish.
MSDE does all of that... for a graphical view of your MSDE database you have to additionally install the manager application which is available.
To put MSDE remote you need to enable protocols during install or via the network configuration utility.
MSDE limits 8 concurrent connections
MSDE database cannot grow beyond 2gb
Those are the biggest limitations of MSDE that I can remember.
Unless your BES is going to have more than 200 users on it, it should be fine to use MSDE.
As far as googling all day... http://www.google.ca/search?sourceid...&q=msde+vs+sql
First result looks good to me