Well, I would argue that that having a pet provides just enough of a distraction to mellow me out when I find myself getting stressed. Watching my cat chase around little toys attached to strings is priceless entertainment and taking care of a pet really doesn't cost that much. There are some downsides though - 1. most nice places to live don't allow pets, so sometimes there's a trade-off there, 2. unlike a girlfriend or boyfriend that you can dump if they get annoying, it's much harder to extricate yourself from an owner-pet relationship if you find that it's more than you can handle, 3. you also have to worry about a pet like you would worry about a toddler - you really can't "go home" or wherever for an extended period of time without making arrangements for the care of your pet, so this really restricts your freedom a bit, 4. cats are a little easier to take care of, but if you get a dog, you HAVE to walk it when it wants to be walked - you're on their timeschedule, not on yours! (or else you're going to have a very messy house!), 5. many people are allergic, so you might want to keep this in mind if you like to entertain or plan on having roommates, 6. as well, many grad student apartments are TINY, so this can be burdensome on a pet if it doesn't have enough room to run around in your apartment, and 7. it's something to think about - it's been my experience from visiting a number of grad student apartments that grad students generally do NOT take care of their pets the way they should regarding cleanliness - most grad students are messy and don't even clean their apartments like they should, so adding a pet to this makes for some very nasty environments. In the end, I think a pet can really add to your overall quality of life as a grad student IFF you are responsible enough to take care of it!!