Had my first WU upload, but it has left behind approx 300Meg of files. Another post suggested this is so they can be interrogated later.

Question is how are they interrogated and how long do they remain on the hard drive. Is there some mechanism for the CP people to request a file be uploaded and to flush all remaining files after a period of time through BOINC.

My main concern is that if each WU leaves 300Meg behind, then you are using Gigs of disk space in less that an year

It is fine to transfer to CD/DVD if HD space is a problem. If you can't, then it's not the end of the world if you have to delete.

THere is no rule about this - the project have been asking for the files from a sample of runs, and these have all been done relatively recently (within two or three months) but it is possible that they could ask for ones done well before.

The other reason for keeping them is personal interest - there are tools such as Martin Sykes's CPView which can be used for studying past runs.

when you set BOINC to use X-units of disk space, it'll ever only use that amount.
If it gets another WU and requires additional disk space to run, its smart enough to delete completed WU's in an intelligent way.