The price of silver is at a 30-year high. One ounce of silver is now trading over $32. The only reason it is not at an all-time high is because of its brief rise to almost $50 back in 1980. That brief explosion in silver prices occurred when the Hunt brothers tried to corner the silver market. It also happened during a time of high inflation and right about the time that Paul Volcker slammed on the monetary brakes.
I am a fan of silver related investments only up to a point. As we can see from 1980, the price of silver can go down just as quickly as it can go up. Silver is far more volatile than gold. For this reason, I suggest that you invest a far higher proportion of your money into gold related investments than silver.
Silver may have a place in your portfolio, but it should be a small place. I wouldn't recommend more than 5%, or maybe 10% if you are really aggressive. It is a good speculation because there is such a high upside potential. If gold goes to $2,000 per ounce in the next year or two, silver could easily go to $75 per ounce or more. This is not a prediction, but just an observation that silver is a higher risk and reward play than gold.
If you are good at timing the market (almost nobody is), then silver is a stronger play. If you invest in it as a speculation, try to be disciplined and take some profits if and when the price goes up. You will never know exactly when it will reach its top, just like any other investment. It is important not to get too greedy and to take profits on the way up. It doesn't mean you have to sell all of it at once. Actually, it is a good idea if you don't.
Again, I am talking about silver and silver related investments here as a speculation. It should not be part of your permanent portfolio. For Harry Browne's permanent portfolio, the gold portion will be your protection against inflation and a crashing dollar. Gold is far more stable than silver and I expect it to continue that way.