She may be only about a year old, but Maggie contributes as much to a Simpsons episode as any other character. Being so young, It's not clear what she thinks about much, as she is only able to communicate through whimpers, crying and the suck-sucks from her pacifier. That is, she is only able to communicate with humans through these means. She has no problems with other babies. And Bears. Its clear that she says nothing, but understands everything. She could, on reflection, be even smarter than Lisa. After all, she created a sucessful plan to rescue the baby's pacifiers without any military training in "A Streetcar Named Marge", understands what "credenza" means, and now knows the difference between "Aztec" and "Omec", and I don't even know what an Omec is, though I presume it's a lot like an Aztec. Not bad for a baby.
And thats about as much as I can say. Maggie has so-far led a simple life, allowing Marge to worry about her health, sanitary condition and clothing. Aside from nearly murdering Mr Burns(and nearly getting away with it too, if it hadn't been for that darn sister of hers), and the adformentioned pacifier rescue, Maggie hasn't seen much action, and will probably see little more until she enters Kindergarten, where her adventures will really begin... Maggie seems to combine both her sisters intelligence and her brothers sense of adventure, but promises to be quite differn't from either of her siblings.
Future Echoes
As far as I know, only "Lisa's Wedding" has shown us what a future Maggie may be like. At 16 years old, we're told she's something of chatterbox, although we never hear her speak of course. A constant running joke through this episode, Maggie is repeatedly interrupted whenever she opens her mouth - shame, as we almost got to hear her sing "Amazing Grace"! She seems to like motorbikes, and is a phone lead twiddler like her mum(she also has Lisa's old room)