Here are some metrics that I would want to know about to measure user-engagement for a file storage and sharing platform similar to Dropbox:
- Unique user accounts (UU): Technically, just the number of sign-ups is not a user-engagement metric, but this is definitely an important success metric, and a foundation stone for future user-engagement.
- Active users (MAU and DAU): A health UU metric is good, but what matters most is how many of these come back frequently. Monthly Active Users (MAU) and Daily Active Users (DAU) are two most popular measures, but depending on your needs, you may have a different level of granularity.
- Upload frequency: For a service like Dropbox, I would like to know how frequently users are actually uploading files to their accounts. An even stronger indicator can be how many users have set-up automatic sync between their devices and the service.
- Content access frequency: Another good user-engagement metric is how frequently the uploaded content is being accessed. This will include downloads and users accessing their content directly on site and others accessing users' shared contentthe ettteteee.
- Storage used: Another user-engagement metric specific to this case would be how much storage is being used. If active users are using up a good share of what is available to them, that is a good sign.
- Upgrades: With so many free storage options available, if your users decide to pay you for more storage, they are definitely engaged!
- Referrals: If users consider your service good enough to be referred to their friends, they definitely like your service. Even if they do this for additional free storage, this is still a strong positive, as this indicates theirs interest in using your service more.
- Device-mix: The mix of devices from which your service is being accessed can tell you a lot about how they intend to use it, and how strong you can expect the future engagement to be. I would definitely want the device mix to have a good representation of mobile (smartphones/tablets), as this indicates users' interest in accessing your service on the go.
In addition to the absolute values of these metrics, the ratios of some of these metrics (Examples: MAU/UU, DAU/UU, DU/MAU, Upgrade/UU etc.) can serve as excellent indicators of user-engagement.