The OP is falling into the classic trap of investing more in something when it's already high. You get drawn in at the peak just before the price plummets.
Gold is an investment like any other. It goes up and it goes down. It's not a bad idea to include it as a part of your investment choices, but only a part. Mix it up with different types of investment vehicles for diversivication.
Gold has done well lately. The value has grown 26% annually from 2005-2008. Hence the ads you've seen. But, it's not unusual for an investment type to have a hot streak like this. So, how has gold performed overall? Well, the recent hot streak is the exception, not the rule.
From 1833 to 1970, the price of gold changed very little. In 1833 it was $20.65/ounce and in 1970 it was $40.80/ounce. From 1930-1970, it grew at an annual rate of 1.7%. After the 70s it did grow faster, at an average of 8.8% from the 70s to the present.
Not terrible but during that time the price has been very volatile. Just huge swings in prices. So, if we're in a huge upswing now, odds are a huge downswing is just around the corner. I don't think I'd want to invest at the market peak!
Mr Awe