It does bring up an interesting issue though - what if someone did set up a botnet, then used it for a generally beneficial purpose... sort of a modern-day take

It does bring up an interesting issue though - what if someone did set up a botnet, then used it for a generally beneficial purpose... sort of a modern-day take on robin hood... This would be quite different to SETI or other similar distributed-processing apps, as it spreads itself without user intervention / specific installation. If this was used for some useful purpose (eg auto-mirroring content based on current traffic) I could see some very interesting possibilities. However - the temptation to subvert it for nefarious purposes once it is up and running is likely to be too great for it to last long...