Depending on the species, having two companion birds can actually change their personalities. Do you want the bird to be friends with you mostly, or with another bird mostly? If you're going for something like a cockatiel or budgie, it could be harder to hand-train them if they have a buddy to play with that looks more like them. If they're going to be spending a lot of time in their cages, you might want to get two so they have someone else to talk to while you're doing other things. My cockatiel is a single, and I got him before I had any other birds, and he is attached to me like no other, but my aunt's old budgies were in pairs and they didn't care about being out of the cage ever as long as they had each other (and they'd attack you if you tried to get them out). That being said, I think that's kind of like keeping a lone rat - to me personally, it seems pretty cruel, but I'm big on wearing my birds around the house. I work full-time (40+ hours) and go to school (online) full-time and my birds are fine while the house is empty - but I make it up to them on my days off and let them out all day long, so as long as you give them SOME time and don't leave them in the cage from sun-up to sun-down seven days a week, you'll be fine leaving them alone for 5-8 hours 4 days a week.

Another thing you'll want to be careful of around the house that I don't know if anyone previously mentioned or not is fans - ceiling and otherwise. I've known people whose birds have been accidentally amputated or killed because they didn't clip their birds' wings at all and let them fly around the house with a ceiling fan on. I had someone email me late at night asking for some birdy first-aid tips to keep his bird alive until he could get to the vet because his 'tiel lost a wing in the ceiling fan (it literally amputated the bird's wing right off), so if you've got them and you use them, either turn them off while the birds are out or do a partial wing-clip (so they can't get much height but can still flutter around with ease) - or don't take the birds out while the fan has to be on. Also be careful with heating and air conditioning vents - think about cage placement; if they have a draft on them, hot or cold, it can lead to illness. Same thing if they're too close to a window during extreme weather. If their cage is in another room in the house and they hear you, they're going to try to shout for you or get out and come see you, so make sure they're right in the middle of everything where they like to be.

Having a bird is like having a perpetual 1-year-old - literally, my 1-year-old niece came to visit recently and she found every single thing I'd finally hidden from my birds and started putting it into her mouth or tearing it just like my birds were trying to do with it. Most parrot-family birds live between 15 and 125 years of age, so choose very carefully, make sure you are ready for the challenge (just like having a kid, but less labor pains), and spend some time hanging around with your prospective bird choices before you decide for sure - find one that takes to you as much as you take to it, and you can't go wrong.

Birds are a real treat, and I hope you find a darling forever feathered-kid to share your life with