I've got a lot of pros:
They're SEMI-nocturnal. My (well DD1's, but I love it so much, mad crazy hamster woman that I am) hamster is currently playing very happily on my lap. It's 4:49 at the mo, and she woke up as soon as I got home because she loves coming out.
Easy to play with while watching TV. Biggest play time for our hamster is watching either Merlin, or a TV film etc;
Loving!
Everyone said DD1 would be bored of her. They told me before we got our hamster (called Molly). I'd do the cleaning out etc; Nope! DD1 cleans the cage out once a week, the bedding more than twice a week, water every day, sometimes every two days, food every day, and goes down to Pets At Home on the way back from school, where she might either buy food or spend her pocket money on treats for the hamster, or an exercise ball.
Cons:
Have to sort out in the holidays who's looking after it!
They die quickly. Our one is currently a year old. That's the longest so far. The dwarf hamsters (Chinese, wouldn't reccommend one for anyone who hasn;t had Syrian hamsters) are also coming up to a year. When the hamsters have previously die, we had a DD1 struggling through tears, a midnight (they ALWAYS die just before I go to bed and check on the hamster to say goodnight and find it stiff in its wheel) burial etc; and strict mourning.
If you want a snippet of how much DD1 loves her hamsters, this is her christmas list-
New hamster cage, for my biggest present please, but if it's too big or expensive, some tubes would be good, thank you.
Hamster treats please, mainly milk or chocolate drops, but dried bananas or apple chews would be fine.
Hamster chew toy or a mineral biter for the hamster.
A toy like a seesaw or tubes for the hamster to go in its cage.
She's got 15 things, and the only one which doesn't involve hamsters is the 'a rat would be nice' at the bottom.