Every method has its strengths and weaknesses. For instance, a strength of DFT is that is has HF like speeds, but can also account for electron-correlation and this is a pretty big feature since methods that account for electron correlation typically either require more than 1 Slater determinant (Configuration Interaction, Coupled Cluster etc.), or involve expensive perturbation about a HF reference system (Many Body Perturbation Theories).
A result of DFT being so pound-for-pound good is that its popularity is soaring.
Given the relative ease in which a DFT calcualtion can be performed, this makes it perfect for "turning the crank".
There are however instances where DFT fails or has caveats.
What are the systems/phenomena/caveats users should be aware of when modelling materials with DFT?
For instance, one caveat I know of is that because of the complexity of the exchange/correlation functionals, they must be numerically integrated. This means a grid-size must be set, and while programs such as Gaussian allow the user to set the grid-size, generally, a default grid-size is used unbeknownst to the novice user.