Flavoured oils

There's something so nostalgic about flavoured oils. They definitely aren't a new aged thing, they were extremely popular in the 70's as decorations, in the 80's home cooks began to use them more regularly, and the 90's saw most "fine food" shops carry the products in mass quantity. I very specifically remember going into Julian Graves in Scotland when I was a teenager and seeing an entire wall full of flavoured oils. By comparison, these days very few food stores carry a great number of the oils and those that do limit their stocks to garlic and chili oil.
This is partly because of the recent trends towards natural foods and foodies seem to prefer the taste and concept of naturally flavoured oils, nut oils for instance, and the need for infused oils is dropping. The flavour imparted by an infused oil like garlic oil does indeed pale in comparison to rubbing a food with garlic, and I agree there's very little reason to use them anymore but I still enjoy making them and I do indeed enjoy using them... sometimes.
Another reason the usage of flavoured oils dropped off was because of the discovery that their shelf life is considerably shorter than unflavoured oils and there is an increased risk of botulism in most oils. That, coupled with the inability of most oils to be refrigerated and the usefulness of flavoured oils is drastically altered.
There are several rules to follow when making, storing, and using flavoured oils.
Firstly, use a sterile container. For this the only suitable substance is glass. It is extremely easy to boil glass for a couple of minutes to kill any bacteria, try and do that with plastic and by the time the plastic cools enough to fill the bacteria have already returned. Metals on the other hand have two perceived disadvantages, firstly they will contaminate the flavour of the oil and give it a semi-rancid taste after long term storage, secondly there is a risk that it can discolour oils flavoured with ingredients like garlic or herbs. That really only leaves glass.
Secondly, heat your oil before storing. This will, once again, kill any bacteria in the oil or ingredients to be infused, and will actually help impart more flavour into your oil. This is especially true with garlic, which was seemingly born to carry botulism.
Third, store your oils properly. This is true for more than just flavoured oils. All oils should be kept in cool dark places, not refrigerated (unless otherwise specified), and always be kept in an airtight container. Failure to do so will make your oils rancid extremely quickly, and rancid oil is both incredibly disgusting and potentially very dangerous for you.
Fourth, know when to throw things out. Again, not just true of oils. If you've had that bottle of truffle oil for six years, throw it out. I don't care how much you paid for it, throw it out. No oil will last forever, try not to keep any oil longer than 6 months. To prevent wastage buy oil in small batches.
Fifth, be aware of the smoking point of the oil your using. Again, this applies to oil in general. The smoke point is the heat at which a fat begins to smoke, a sign that it is beginning to break down chemically and start to taste downright funky. All oils have a smokepoint, you can easily look them up online or in many cookbooks. Try not to heat oil beyond these points, it destroys flavours.
If you do those things you will effectively remove any of the dangers of using flavoured oils.

Flavoured oils are wonderful as simple salad dressings, great for dipping foccacia in, or great for cooking meats in (again, avoiding the smoking point).
To begin your flavoured oil endeavor choose a flavour that you like to infuse the oil with. Popular flavours include garlic, chive, chili, and then of course nut oils, which aren't actually infused (most of the time).
Secondly choose your oil, good oils for most infusions include safflower, peanut, vegetable, or canola oil. Anything neutral really, though there is a time and a place for stronger oils. I personally enjoy garlic infused olive oil, for which I use a virgin grade olive oil which has a slight flavour which won't overpower the garlic.
I generally heat my oils slightly to help the flavours merry and then bottle them. When using herbs you can even blend the herbs with the oil, strain through cheesecloth and then bottle to impart maximum flavour, though I wouldn't use it for cooking.
And do not discount sweeter flavoured oils, a great oil for very lightly dressing fruit salads in is an oil infused with orange peel studded with clove.

If you're interested in making your own infused oils I would recommend going to your local kitchen supply store, picking up a few bottles and spiggets and playing around. You may actually enjoy it.