I just upgraded to the Eris yesterday after comparing the Moto and Eris online and in the stores, and so far I am loving it! I have a LOT to learn, but it's so fun and useful!
My main concern right now is battery life. As it's my first smartphone ever, I am prepared for some battery-life shock, but I do want to be able to rely on the battery to last through my workday (usually about 12-15 hours)... and today that's not looking likely (charged to 100% last night at 9 pm, didn't use it until 5 this morning when it was already slightly depleted... and now at 9 am it's looking like it's at 50%). Does that sound typical?
I welcome any advice, and plan to spend a good amount of time exploring these forms in the next few days/weeks.