• They are low-maintenance. Oh.  This is sooooo wrong!  Birds are complex beings that have special demands and needs that most people don't understand at first.  It is actually fairly challenging to take proper care of a bird.  And then there's the mess.  All birds are messy to some degree.  You'll have seed and discarded food flung everywhere.  Even with potty trained birds, you'll have the occasional accident. 
• They rarely get sick.  Wrong again.  I have to say that the people I know with birds spend a LOT more on vet bills that people with other kinds of pets.  Birds hide their illnesses.  By the time you see symptoms, they are often very, very sick.  For that reason, many bird lovers (including me) advocate an annual "well bird checkup".  That's something most dog/cat owners would never dream of doing.    
• They are easy and cheap to feed, just give them some birdseed.   Birds need a varied diet.  I can't think of any species of bird that will thrive on a seed-only diet.  They also need fresh fruit, veggies, and other perishable foods.  Some species, if improperly fed, will develop nasty behavioral problems that can become chronic.   
• They don't take up a lot of space.  This one can be true if you are cruel and selfish enough to put the bird in a small cage and never let it out for exercise and play.  
• They are a great decorative addition to a room  Ooh, puh-leeze!  If you want something decorative, get a statue, get a painting.  Don't take on a living creature because it's decorative.
• They are a cool.  Too many so-called "bird lovers" are really just wanting a "trophy pet", something that gets ooo's and ahhh's from friends and acquaintances.  
• They talk.  Maybe.  Maybe not.  Not all birds that are capable of talking choose to do so.  Will you still love "Polly" if she never utters a word?  And remember: the bird that chooses to talk is going to talk.  And talk....and talk.  There's no "off button" so be careful what you wish for.  
• They can learn tricks.  As with talking, some do and some don't.
• They will bond with you.  Yes - quite probably.  But will you bond with them?

All birds have a "down side".  Before you adopt, educate yourself on what that means for the species you are interested in.  Here's a short list of "down side" items that I'm aware of for various types:

MACAW

• Loud.  Really loud.  Can damage your hearing 
• Must be kept amused and stimulated.  Bored macaws go crazy.  A crazy large bird is not a good thing.
• at sexual maturity (4-6 yrs) hormones kick in and your sweet cuddly baby is likely to change.  Many macaws are re-homed at ages 4-6.
• some species are nippier than others, but all can inflict a nasty bite.
• destructive.  Will eat your furniture, your walls, anything they can get to.
• very active bird that needs lots of exercise for muscle tone and also to work off "steam".  This is not a bird that will sit quietly on a T-stand.
• must have lots of human interaction, especially early on.  Need to be taught good social skills (ie: allow handling by many different people) early on so that they don't become a 'one person bird'
• loves to throw food around the room.
• smart enough to be able to unlock it's own cage
• needs 10-12 hours of dark and quiet every night in order to get enough sleep.  Inadequate sleep = cranky bird.

ECLECTUS

• Loud.  Really loud.  Can damage your hearing 
• during breeding season (which apparently is 11 months out of the year...) becomes very moody.  At the age of 3 our ekkie George selected me to be his "special loved one" and from then on has bitten me quite badly more times than I can count.
• body language for ekkies seems to be very, very subtle (at least I think it's subtle).  Because they are hard to "read", it's harder to know when the bird is angry/upset enough to bite.
• diet is an issue for ekkies.  They are very sensitive to too much of this and not enough of that.  Diet for these birds is apparently not well understood and there's a lot of bad (and conflicting) advice out there.

QUAKERS

• tend to become very territorial about the cage.  Cleaning and otherwise servicing the cage may be impossible unless the bird is taken out and removed from the room beforehand 
• can bond too tightly to one person and reject (bite) all other comers

BUDGIES

• for such a small bird, unbelievably messy.  From what I've seen, 1 budgie makes the same mess as 2 cockatiels.  They just seem to love throwing seed and what-not all over.  

LOVE BIRDS

• can be screechy in a high-pitched and annoying way

SUN CONURES

• Loud.  Really loud.  And shrill.  I'd rather here my macaw scream than a sun conure. 
• Demanding.  Once they bond to you, they want to be with you constantly.  If you don't comply... you get screaming.
• All conures seem to think that hanging on the side of the cage and expelling their poo so that it lands on the floor beyond the cage is great fun.

GREEN CHEEK, BLACK CAP,  AND MAROON-BELLIED CONURES

• Go through a nippy stage within the first 12 months.  Some get over it, some don't.
• All conures seem to think that hanging on the side of the cage and expelling their poo so that it lands on the floor beyond the cage is great fun.

COCKATIELS

• If handled consistently from rearing, they are normally quite docile - but some individuals can be pretty nippy.