I would really like to know to where Project Rosetta stores the datasets that it downloads. Each task download is about 230MB, which is something large for me.
I want to know whether BOINC deletes the data set after the processing is done, or do they linger around forever?

I am actively using the system, so it's necessary for me to know how much memory space is available on my root and home partitions

The files are stored in /var/lib/boinc-client/slots/ on Ubuntu

Then depending on how many cpu's you have there will be a slot for each cpu.