Remus is correct...it appeared with the PS CS versions.
However, you can achieve the same effects by using the "depth mask" as an alpha channel and (depending on what you want to do...make the near blurred or the far blurred) simply use Gausian blur to throw the area "out of focus." In fact, this will also work with other image editors such as GIMP (which incidentally has a Gausian filter capable of finer tuning than Photoshop's).
The Photoshop CS lens blur filter complicates matters needlessly. I almost never use it.
Incidentally, once you have a depth mask as an alpha channel, you can control its relative strength using Levels on the channel. Want things to get blurry real fast, as if you used a telescopic lens? Increase the contrast in the depth mask channel.
I also use depth mask channels to simulate the watercolorist's traditional "atmospheric perspective"--in other words, things that are far away are more gray (desaturated) compared to foreground objects.
If I have a little time later today I'll post some examples.
