Memory Cards have been around for quite a few years and come in a variety of capacities and sizes and speeds. Essentially they are a version of a floppy disk used years ago in desktop computers (without the spinning disks of course). They have a specific file directory that tells your computer where a particular image may be found on the card. Without doubt, they can carry some very valuable information within our cameras and phones but are fragile to say the least. There are some things that we can all do to protect the data and the card itself against data loss.
One of the simplest and least expensive things we can do is put them in a case. Several years ago SanDisk would ship each card with it's own case to protect it but that practice has stopped. Placing cards in your pocketor loose in a camera bag with other equipment is begging to have the metal contacts on the card (or the card itself damaged). Hard cases are very inexpensive through sites such as Amazon.
Formatting cards within the camera that they are being used in can be valuable. Formatting creates a new file system and of course deletes any information stored prior to that point on the card. If you format a card within the camera that you plan to use, you are creating an ideal system for that can be accessed by your camera. Simply deleting files from your computer or camera can leave gaps in the file structure that can cause read/write delays or even data loss over a period of time. Sharing cards from different cameras can also issues due to the unique method the file directory has been created.
Is the fastest card always the best? Not really, but it all depends on what you are planning to shoot. If you are shooting video or action photography then of course a fast card is important. Are you shooting product photography on the other hand you probably paying for something that you may never need. Another point is to look at what your camera is capable of handing in terms of card type and speed? The card still may work in your camera, although once again you are paying for more than what you may need or worse yet, it may not work at all!
Should one buy the super high capacity card for an upcoming project? Well this in part depending how you have your camera set to produce image files followed by what you plan after the project. Raw files will typically take up more space than JPEGs and if you have set your camera to the largest size possible, then the card will obviously fill up faster. If you need to immediately hand your card over to an editor staff (similar to some sports photographers) then handing the staff a dozen cards will not be your best bet. Even so, a 64 or 128 Mbyte card will hold quite a few images (a 128 mgbyte card will easily hold thousands of images). The down side to cards with even higher capacities (apart from cost) may be if the card is damaged or lost, the entire photoshoot may be lost!
So how long do cards last? It depends on how often you use the card and how you handle it. If you are photographer who shoots several times per week every week, it maybe good practice to buy new cards every year. On the other hand, if you are an occasional photographer who may shoot once per month, a card could last 2 or more years. A general rule of thumb however may be 'how important is the project'? If you are shooting a wedding professionally with a card 2 or more years old, you are taking a risk.
What about the microcards in adapters? Microcards are great for gaming systems, cell phones, and even music players. Will they work in standard DSLR or mirrorless cameras? Of course, but keep in mind that you are adding additional hardware and if the microcard is not inserted properly, damage could occur. Micro cards outside of the adapter are VERY easy to loose!
As with most things, what you choose to buy depends on your needs or wants. Most photographers will want to purchase cards from a known brand that have a track history of reliability. Even a vacation memory can be valuable to most of us.