rusty's response was perfect... + a major 1 to his post.
One thing I would add, Blackberry is not very "linked" to any one particular email account. Android devices are. Your "talk" account (think BBM) your latitude location (on google maps), your market account (where you download and pay for apps) - they're all linked irrevocably to one particular gmail account.
I was NOT a gmail user prior to getting my Droid. When I was in the store buying the Droid the salesperson asked rather casually, "do you have a gmail acount?". I remembered I DID have an old one from an old job. I hadn't used it for years and no friends or family had it. I remembered the password and he set it up for me. Within a week I got tired of using that old email address and made a new one -- tough luck. There is no switching. I had to do complete wipe and factory reset, in order to "link" it as the primary bemail address - what a pain.
So, my advice: take your time and set up a really good gmail address you'll be happy being married to for a loooong time.