Have found it useful in the hospital I work for pointing to a web page were
patients can download patient information. Saving time and printing costs of
leaflets etc.

I just returned from a national conference. A federal agency who had many
representatives there instructed their people not to hand out business cards
(which they said is a low tech way to do business in a high tech world).
Instead, their people had their contact information on their phones in the
form of a QR code. Those who wanted to connect with them had to have a smart
phone and an app to scan the codes. It was inconvenient and time consuming,
but it did require more conversation with the person rather than just handing
out a card and moving on, so the contacts may have been better. Time will
tell.

QR codes are not very popular, and there is a big chance that they will
disappear. They are great for barcode replacement but I don't see them pickup
in online marketing for the following reasons:
1. They are very clumsy, it is not easy to point your phone and hold it
steady so you can take a proper scan of a QR code.
2. QR codes can be a source for viruses and malware to your phone. How would
you know that the QR code you are scanning does not point to a malicious url?
you don't. Hence it is better to avoid scanning random codes.

Most industry experts predict that NFC will soon replace QR codes, since they
are easier to scan and are not as easy to use for pointing to malicious
software.

I have considered it, but I don't use them. I haven't found enough people who
have installed the apps to read the codes. However, my friend who is a real
estate agent, uses them on the flyers for the homes she has under contract.
She has found them to be helpful in "pre-qualifying" potential buyers.