After reading the offline thread,it reminded me of some of the discussions here about bringing a corked or damaged bottle ( undrinkable ) to a dinner where everyone is supposed to contribute.Whats the general consensus on whether that counts or participants should always have a back up or 2 ? ( of course this can be avoided if you decant and taste the wine ) before coming. I’ve always been a believer in having back ups…
I agree- either open in advance or bring a back up is the best advice
This.
I always tote 2-3 bottles to every offline just in case.
Bring a back-up, always. But if something goes wrong, I don’t sweat it. Happens to all of us, we all have a dud on occasion. I would not enjoy my group if I sweated whether there was perfect quid pro quo.
I suppose it’s nice to have a backup, but I hope we aren’t really keeping score. I haven’t been to one yet where we had too little wine.
If possible, it is always nice to bring a backup. That said, if I am flying in and bringing wine on a trip, that is the one situation where I don’t. It is always a struggle as it is to have luggage room, and the last thing you want is to travel BACK home with unopened backups.
More is always better. I always bring a couple bottles.
Good point Eric, matter of fact, if a friend was coming from oot, I’d probably be bringing one to cover him anyway. Most people don’t carry wine on a trip, unless it was specifically for the wine dinner. Of course there are some of us the just ship their wine in advance…
Just buy a bottle off the list
To me, requiring or expecting everyone to bring backups is a bit much.
If it is a new(er) vintage of a wine, the chances of something being wrong with it seem lower, so I wouldn’t expect backups.
If it is an old and/or rare wine, I typically feel bad for person who opened it, and would feel worse by pressuring them into another equal bottle.
Does it make a difference if the bottle is corked or just isn’t any good (over the hill, bad storage, etc.)? I guess my point is that I may bring a backup, or others may bring backups, but I would always consider that a bonus, not a requirement. I would be more likely to brink backup if I had doubts about the first bottle I brought for one reason or another. Ultimately they brought something and opened it to share, maybe it is your fault if you don’t want to drink it. . . 
+1
I bring backup. Lance, my buddy uses his Coravin.
Lance is smarter than I, PLUS he owns a Coravin…
…and he hasn’t given one to you for your birthday yet? Shame!
What Eric said—if I’m traveling I’m not going to sweat bringing a backup to an oot dinner. OTOH, on the upcoming Cali trip, it does look like I’m toting 9 or 10 bottles with me from my cellar for various events/people 
If I’m in Toronto with my usual group, I won’t bring a backup—we all are OK with it. If I’m out with a bigger group, I will almost always bring a backup–usually because we have flights going and want to get the value of that.
Coravin the bottle before you leave the house to check for flaws. If the wine is good, you’re out a tiny amount and can pop the cork with friends. If the wine is bad, you can return it to the source with unassailable evidence.
I agree with this.
In general, I don’t like drinking with people who keep score.
I always bring a backup, though the backup may be an understudy, not a clone of the lead. For example, if it is a First Growth Bordeaux tasting and I’m bringing a Lafite, the backup may be a Lynch Bages, a Montrose, or a Leoville-*.
In large part that is because if the way my cellar is organized, and just because I can get to one bottle of a given wine doesn’t mean I can get to another without moving dozens of cases in a cramped space. Or I may not have another bottle of the same wine.
But a balancing of the equities also comes into play. This may be a little selfish, but if I bring an expensive bottle that is corked, I’m out the money often without recourse, and it doesn’t seem reasonable to be expected to contribute two very expensive wines. On the other hand, the rest of the group is also deprived of a wine I committed to bring, even though it was beyond my control. So, to me, it seems fair to both sides to bring a backup that isn’t grossly out of place with the theme and, though it may not be as expensive or prestigious as the lead, it is still very good and may be better than other on theme wines (which may include the lead whose role the understudy is playing).
Of course, the Portuguese Scourge can wreck even the best of intentions. I’ll never forget a dinner where one attendee was so upset that his magnum of 1966 or 1970 Latour was corked that he ran home and brought back a magnum of 1982 Mouton as a replacement, which I think was above and beyond what would be reasonably expected. We jokingly chided him for not opening the wine to check it before he came back. But our jibes turned to sincere condolences and heartfelt thanks for his generosity when it also turned out to be corked. That served as a practice run for our reaction when a magnum of 1945 Latour with pristine provenance that a friend had gone through great efforts and expense to get to share with us was also corked. He didn’t bring a backup, and if anyone there had suggested that he should have, I think the rest of us would have unceremoniously carried the critic from the room and deposited him in the dirtiest, smelliest dumpster we could find.
Some would say that’s unethical!
At the wine parties I attend, most people usually bring more than one bottle. Frankly, it’s more often the case that TOO MANY bottles get opened than too few. I’ve had to tell people not to open a second or third bottle at some of my wine dinners because it’s just too damn much wine (yes, that is possible).
It’s more of a challenge when you have a tightly-organized tasting–like a vertical of a particular winery–and one of the bottles is corked. If someone has multiple bottles of the vintage they’re bringing, a backup is nice. But if your 1989 Haut Brion is corked, I don’t expect someone to bring a backup 89 Haut Brion…
Bruce
Is there really any reason not to check out the wine beforehand? I never bring anything to a local gathering I haven’t at least checked out , if not cleaned and aerated.
I do understand if you’re flying…that might change things a bit…but…flying/shaking shortly before serving can’t help a wine show well at any rate.