the simple way to see if you are suffering a memory leak is checking "/showmem 1", mine nearly always stays around 730-750MB, also you could alt+tab and go to taskmanager, if you are seeing the "gameclient.exe" hit 4GB or close to that (because it's a 32bit application it can't go any more than that, even if you are running a 64bit machine (hence the "*32" next to the filename) then yes you may have a memory leak,

I personally am not, but I have suffered the framerate drop on Nukara, as I did in Tribble (which I also reported),

but the interesting thing I noted was popping into the caves reset the framerate issue for me, also I noted every time I died it got worse until I went into the caves,

so read into that what you will

/also for the record I'm running an AMD 1090t Black Edition (overclocked to 4.0Ghz), 16GB of RAM, nVidia GTX580 (1.5GB)

also, I have not been to Nukara since the new nVidia drivers came out