It may seem that my answer is hedging a bit, but I think any restrictions on civil liberties, while perhaps necessary, ought to be subject to very strict scrutiny. Once they are gone, they have a way of not being recovered again due to legal precedent. Ordering military strikes against US citizens, for example, or imprisoning them as "enemy combatants" creates very disturbing precedents. So do some of the surveillance provisions of the Patriot Act. Again, I don't think we can say on face of it that these changes are unnecessary, just that they ought to have to pass the most stern constitutional tests perhaps even before they are instituted.

There is certainly a point of balance between liberty and security. However, I do agree with Ben Franklin. Too many are willing to hand over their freedom in exchange for security without realizing what the consequences will be. While I do not think we have currently lost any of our constitutional freedoms, there are a few n security measures that are right on the line. There have certainly been some changes that effect the way we think of our freedom. There are some rights that we may have thought we had that have changed. 

Benjamin Franklin is roughly quoted as saying those who would give up their liberty for security deserve neither.  I agree with Ben completely.  The moment when we give up our liberties to ensure our protection is the moment when we decide there are more important things than freedom.  Once our protection is gained, that freedom is highly unlikely to be given back.

It seems more likely that Canada has suffered no terrorist attacks because it is not the international hegemon that the US is.  It's not as if the US was oppressing Muslims here in our country before 9/11.

As to the question of the Bill of Rights, there is always a balance between civil liberties and order.  We never have the complete right to free speech (we can't threaten others, for example).  It is reasonable, in my mind, to shift the balance to some degree away from liberty and towards order in our current situation.  This does not mean that we throw away all liberties, it means that we accept some reductions of liberty for our safety.

Of course, this is a slippery slope.  It is very hard to know how much (if at all) our safety improves if we lose some of our rights so that the government can do more surveillance.  We cannot set any bright line and know that that is exactly how much in the way of rights we can afford to lose.

In theory, it makes sense to have our rights restricted.  In practice, it is very hard to know how much restriction to accept.

My own sense is that rights should not be restructed or we become precisely the sort of tyrrany we claim to be fighting against. Also, there is no evidence that the restrictions actually have made us safer. The terrorists who have been caught have generally been caught through espionage -- not through forbidding people to carry water bottles through airport security. Many of the elements of the Patriot Act are pandering to the worst forms of racism and paranoia.

In Canada, one reason there have been no terrorist attacks is that the Muslim community feels welcom rather than victimized and the few people weho have plotted criminal attacks have been immediately turned in to the authorities.