Lots of answers from the experienced members...most of them encouraging to me since I consider myself in the league of enthusiastic newbies eager to learn...
However since you asked about experiences as well I have experienced buddies from both ends of the spectrum in my first two certified dives.
I was certified in Aruba and had completed my final checkout dive in the first of a 2 tank dive trip.
On the second dive (my first certified dive) my instructor paired me up with a guy whom he apparently knew pretty well (Ron from FL). He was a great buddy, both for a newbie and, based on what I've read here, in general. He checked out my gear and made sure I was ready before heading into the water, he stayed with me throughout the dive and even helped by pointing out things of interest. We dived on two wrecks...both of them had very simple and short swim-throughs. This guy helped me through the first one by helping me get trimmed out and pointing out that, with a tank and such on my back, I needed to be a bit lower than I was...he pointed this out by physically moving me down. When we got to the second (A plane that was intact but completely empty) and I declined to swim through as I didn't feel my buoyancy control was up to this one (a little longer swim through, uphill, and a bit less open at the entry and exits). Bottom line is he never left my side, was paying attention, and appeared to genuinely enjoy showing the new guy the ropes. When we got back in the boat he complimented me on how well I was doing and offered a few pointers on buoyancy and breathing ("you are certainly wired for SCUBA but need to work on..."). This will probably stand as one of the best dives I will ever have, all things considered.
The next dive I took was on the same boat but a different trip. This time I got paired up with a guy who clearly wanted nothing to do with the buddy system. He was wearing a rig that was different than any I had seen before and I asked him about it...specifically where was his back-up reg? The look he gave me was somewhere between "who is THIS idiot?" and, well, no that was it...the look was definitely "who IS this idiot?". It was the DM sitting next to him that actually answered...his octo was on his right hip or clipped to his waist belt or somewhere in that general vicinity...I actually don't remember in detail now.
Being absolutely green I was a bit intimidated by this reaction and left him alone, which is what he continued to do for me. When we jumped in the water I made an effort to get and stay near him but was pretty much ignored (still). I spent the entire dive following this a**hole around just off his six and pretty much doing nothing else.
To be honest that reaction had me thinking that the buddy system was like a lot of things in life that you get "trained" to do but everyone subsequently ignores in "real life", I felt silly for having even spoken to the guy.
FWIW my reading on this board has taught me that it was him, not me, on dive #2 and next time I will act accordingly to make sure I have an actual buddy.
Diving with a Good Dive Buddy offers an added safety margin and a more pleasurable dive. Solo diving is taboo even though many divers participate in solo diving (that's another subject). Diving with a Bad Buddy Divers actually lowers the safety margin and degrades the pleasure of the dive.
I am starting this thread for everyone to contribute their ideas on what makes a good dive buddy and to share experiences with good dive buddies and bad dive buddies. I have dove with both types of buddy divers.
I'll start.
I think the first criteria for a good buddy diver is that he/she is a competent independently skillful diver.
When I dive with someone who does not ask about a safety check, can't put on their fins, does not know how to safely enter the surf, and descends like an iron anchor, I know that I have to watch them to make sure they are safe and that I can expect little or no help from them. I will during the dive check on their air and keep a keen eye on them. I always have in the back of my mind, if they have trouble how am I going to get them to the surface safely and to the shore on their feet.
My regular dive buddy is very competent, safe, courteous, and knowledgeable about buddy diving etiquette and safety. I have total faith in him and it is a pleasure to dive with him. We both have confidence in ourselves and each other.
Please add your ideas and experiences regarding "What makes a Good Dive Buddy"?
Some ideas: pre-dive, entry, communication, dive plan, equipment, competence, experience, dive formation ,skills, certification, courtesy etc..