Like many products have started doing, Dropbox now offers a web-based installer for its Windows desktop client and also for Mac. When you click the download link, you get a small installer stub instead of the full-sized installer. That web installer will download the full version of Dropbox to your PC and install it. This is not an issue for users who want to install Dropbox on just one PC, but, if you want to download it once and then install it on multiple PCs, it makes no sense to download it individually on every PC.
If you are a Dropbox user and have an Android phone, here is good news for you: you can get an additional 1 GB of free space for your Dropbox account. Dropbox is currently providing it as a gift for new Mailbox for Android app users. Get it while it lasts.