How is SSD lifetime affected by usage pattern and amount of free space?

It is known that SSDs are relatively very limited in the number of writes they can take before starting to slow down or otherwise deteriorate.

Suppose I have a 250GB SSD with 225GB of files which are seldom modified (like system files) and 25GB containing short-lived data (like a downloaded movie that gets deleted soon after watching it) and some free space.

Does all of the new data get written to the same physical components of those 25GB, i.e. "wearing out" this fraction of the SSD very rapidly while the other 90% of the drive hardly gets worn out at all? Or are newer SSDs (or perhaps certain operating systems) smart enough to recognize long-lived data and move it around so that the writes of short-lived data are more evenly spread across the entire drive?

Most modern SSDs utilize a wear leveling technique called 'static wear leveling', where data that does not change is periodically moved, so that the lower-usage cells of the flash memory can be used. In other words, your static data will be moved every so often, so that your short-lived data will wear out other blocks on the drive.

See the Wikipedia article on wear leveling for more information.

All modern SSDs have wear-leveling.