In terms on an investment, how reliable exactly is gold bullion? (and other metals)?

Over the past couple of years, I have heard all kinds of horror stories about pension companies going bust, governments extending the age of retirement, and other such stories. This has got me thinking about my own retirement. While I am still only 27 years old, I realize the way I live my life is going to make it very hard to get good security in my old age, I have moved from country to country a couple of times, and probably will do so again in the years to come, and I have no problem being paid in cash without letting the tax man know from time to time.

I have been looking in to bullion, but all the positive reviews on buying gold and other metals I have found are usually by people who just happen to have some to sell. So I was curious to see if I could get any independent information on the topic.

I am mainly looking in to gold at the moment, but also interested in silver, platinum, palladium, and maybe even copper and titanium or other metals. Do you have any experience with this kind of thing? Is investing in gold as secure as they say it is? What is its track record for staying ahead of inflation? Is there anything else I should know?

note: I’m not rich, you can buy the stuff in bars as little as 1 gram all the way up to 12.5 kilo ingots. Personally I fall in to the 10 to 20 gram category in the form of sporadic purchases.