I've previously suggested you should format your memory card using your digital camera's format command rather than simply deleting the photos. In fact, some photo pros format their card each and every time they are done taking a batch of photos. (I am not that much of a stickler.)
It's really just a question of performance. Memory cards are like hard drives in that they get fragmented when you repeatedly store and erase lots of files. There's no way to defragment a memory card, so formatting it serves that purpose.
A secondary reason to format your memory card is to prevent data corruption. Personally, I've never seen this happen, but I've read many accounts of people seeing weird behavior when they go too long between card formats, and especially if they share a single memory card among more than camera. Indeed, even a few Digital Focus readers chimed in to say they've encountered corrupted cards--which a format fixed. Formatting is no more difficult to do than deleting images, so I recommend it as a best practice.
Will Formatting Reset My File Names?
Some folks worry that formatting their memory card will reset the file-naming counter in the camera, giving them duplicate file names when the photos are copied to the PC.
This is a valid concern, but it depends upon your camera. Some models will remember the number in the file name and continue incrementing after a format, but others won't--they'll restart from 0001 every time you format.
That's frustrating, but even so, it's probably not a show stopper for most people. After all, do you really store all of your digital photos in the same gigantic folder, where duplicate file names would be a problem? Probably not. Most of us keep each photo session in its own unique folder, and most programs that copy photos from the camera to the PC (such as the Photo Import wizard in Windows Vista and Windows 7) create unique folders for each photo session automatically. So even if you have a dozen photos on your computer called DSC00001.JPG, they're all safely segregated from one another. I've worked this way for years and never had a problem.
At least one reader was dubious that anyone would still use a memory card after 8 or 10 years, given the pace of innovation.
That's a fair objection, but I still think my suggestion is worthwhile. For example, I have a 4GB card that I've been using for 5 years now. The 4GB card was a bit pricey when I bought it 5 years ago, but it's still considered a typical size today, and in fact probably will be for years to come.
So, absolutely: I think that it's perfectly reasonable to expect to get 8 years out of a memory card. Moreover, I don't really expect all of us to be using terabyte-sized memory cards in 3 or 4 years. We've reached a point at which most of us have no practical need for beefier memory cards than what you can buy today, and that's unlikely to change any time soon.
Using Several Small Cards
A couple of readers asked me what I thought about the strategy of using several small cards instead of one large one, especially on a vacation or some other important photo trip. The theory: It's cheap insurance, since one corrupt card won't take down all of your pictures, only some of them.
I've know some people use that strategy, but I'm not a fan. It might be cheap insurance, but it's not practical, at least for me. After all, consider the pros and cons. You have to juggle several cards instead of one. You have to keep track of them. You must swap them out as they get full, which is a pain and can cost you a great photo if you run out of space on a card at just the wrong moment.
Now, consider the unlikely situation that one of the cards does fail: You've lost all the photos on that particular card. Sure, you have the rest of your photos, but the more cards you have, ironically, the more probable it is that one of them will fail. That's just basic engineering reliability--the larger your sample size, the more likely you'll encounter a failure.
That's a lot of trouble to go through to prevent a catastrophic failure that, given the reliability of modern memory cards, is incredibly unlikely to happen to begin with. So sure, if it does happen, it's going to be a really, really bad day. But personally, I'm willing to take that risk.
Practically Indestructible Memory Cards
How long will cards last? Reader Adam Samuels sent me a story about a couple who lost their digital camera overboard while on an ocean cruise. The camera was found in the nets of a fishing boat about a year later. The ship's captain reviewed the photos on the card and posted them online to track down the owners, and eventually returned the camera to the couple who lost it. Bottom line: If a memory card can survive a stint on the bottom of the Atlantic, it can probably handle anything you can throw at it.