how important

How important is it to know several standard chess openings when your opponent does notfollow the standard chess oppening you expect from say Eric Schiller's book on standard chess oppenings?

Simple answer: The further you are (ratings wise) from a Federation-rated Expert (USCF 2000 for example), the less important openings are for your development.

Do whatever's fun for you, but if you're under 2000 and want to be efficient about improving/getting better, opening study is FAR down on the list of things you need to take care of.

This advice may sting and 99% of the time, people HATE being told that they are idiots for diving into an opening book when the rest of their chess is suffering ... but it's worth a shot.

Thanks for a great answer.

In anything under expert play, I would say that knowing certain openings is almost pointless. However, that doesn't mean you shouldn't study them.

If your ultimate goal is to reach Master level, opening knowledge will be required. To truly understand and carryout the ideas and strategies behind different openings requires a high level of chess knowledge.

But if you wait until you reach Expert to start studying openings, it may take longer to get over the hump to Master level. I think a better idea that has been recommended by several NMs is to slowly memorize opening lines during your path to improvement. A good way to do this is after you finish a game, look up the opening you played and see where your last "book" move was and compare your the next move you made to the mainline in the book. If you do this and memorize it, you will slowly accumulate 1 book move per game, without "wasting" a lot of time memorizing many opening lines all at once. 

Eventually when you reach a level of pay where openings are important, you presumably will have played thousands of games and should then know many mainlines to most major openings, and hopefully understand some them too.

Well said!  This would be the only approach that I could see a player starting out doing that would be beneficial.  A peek into the book of opening wonders and retrieving ONLY "one" move to add to your organically growing repertoire is where it should be at. If you want to learn 10 new opening moves, you better cough up 10 serious slow games to earn that right. Of course => It helps if those 10 serious slow games get studied, analyzed by a stronger player who writes you a prescription of what you need to do better.

I said this before, but I think understanding key openings and their pawn structures and strategies is extremely helpful to understanding chess. Also, by trying to explore openings a bit yourself (even coming up with your own analysis to be compared to theory) you train yourself in analysis skill (and in this case it's very broad, involving tactics, strategy, everything). This is currently a pretty big part of what I'm doing now to further improve, and many of the openings I'm looking at I don't even play. I also find it really fun. I think it's good for people who are already at the intermediate level, not so much for anyone below that. I think this is a new and strange method for improving, but I think it really helps for people who aren't naturally talented enough to become a GM in a few years. It is strange how people like Fischer just seemed to be extremely good and didn't do any weird techniques though!

To be honest learning openings like the french and queen's gambit (and annotating games played in them) along with silman's books were the main parts of my improvement in strategy.

So, if done right (which is hard) I think openings aren't even much behind the other stuff. I wouldn't be suprised if many people disagreed there, but all I know is it helped me, and it is continuing to help me.

good answer

Really good.