Quote Originally Posted by spenser
From your answers, I infer that according to strict grammar rules (or at least from the point of prescriptive rules), "are" should be the correct verb. However, modern usage has permitted the use of "is". Am I right?
Yes- grammar in the past tended much more owards telling people what they should say, while nowadays there is a far greater emphasis on analysing what people actually use and synthesing rules based on usage. With the example given, I would use 'is' quite happily.

Quote Originally Posted by spenser
I believe this is quite similar to the usage of "fewer/less". During my school days, I learnt that anything that is countable should be quantified by "fewer", and the rest by "less". But today, people are not generally concerned about this distinction. For instance,

"...possibly less than 100 agencies are operating...."

This has always been used in regional varieties of English, and is becoming more and more widespread. Oxford still describe is as a 'dipsuted' usage, which means they won't say it's wrong, but do recognise that many still object to it.

Quote Originally Posted by spenser
In the above sentence, I have now been told that "less" is acceptable; and some quarters even think that, that is the only correct form. By the same token, while I write, "You see, the problem can be solved if either of you is pious or religious. But the problem is, neither of you is.", my friend replaces "is" with "are". I go by the grammar that I was taught, but he goes by what, he says, is "natural".
Again, another area where the rules are relaxing. Traditionally, the singular was favoured as it's negative, but many people feel happier with the plural. I would use the singular in formal language and the plural informally.

Quote Originally Posted by spenser
Please correct me if I am wrong. Once again, I thank you for putting up with me.
It's what the forum is for- we enjoy chatting about language- 'the intolerable wrestle with words and meanings', as TS Eliot famously described it.