I'm doing photo connect for the first time as well so most of my information is coming from another site. (If you google Universal star card FAQ, the first 5 or 6 links have great information).
In general, unlike Disney, Universal doesn't keep your pictures long term if you don't buy a package. So some time during you're first day, you need to stop by and turn in your voucher (if you purchased online) and get your pictured put into your "permanent account" and get you're "permanent" card. With Universal, you can access your pictures online "forever" with the package purchase. Also, if you have a picture you like (that's not HP) for $5 you can get it on a hard plastic Star card.
Another difference I've read between Disney and Universal is in the area of "Magic shot". At Universal, the magic doesn't happen automatically. Sometime towards the end of the day you'll want to go to a photo store and get all of the magic and boarders added to your pictures. That includes replacing the green screen in pictures like the Simpson's Cough Gag hot set with the appropriate background (right now they have 5 or 6 couch gags to choose from).
Another difference is getting prints. At Universal, you can get discounted prints of any of your pictures (except Harry Potter) at any photo shop. They are currently $2 for a 4x6, $5 for a 5x7 and $10 for an 8x10. The photos you download with your packages have been reduced to about 2mp. So they are best for online and 4x6 prints. As was previously mention, high resolution files for printing are only guaranteed to be available onsite the day the picture was taken. Although I've read you may be able to go back a day or 2.