I can only speak from my own experience here rds100. Maybe my customers decide to actually use what they purchase.And to continue about the RAM. Here is an example from a mostly idle test KVM machine i have. This is what is seen inside the VM:
top - 13:21:23 up 22:43, 1 user, load average: 0.00, 0.00, 0.00
Tasks: 52 total, 1 running, 51 sleeping, 0 stopped, 0 zombie
Cpu(s): 0.0%us, 0.3%sy, 0.0%ni, 99.7%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0%st
Mem: 514728k total, 85604k used, 429124k free, 19556k buffers
Swap: 498680k total, 0k used, 498680k free, 50376k cached
On the node the KVM process for this VM has vsize of 584868 KB and RSS of 96652KB.
So this 512MB KVM virtual machine is consuming slightly less than 100MB real RAM on the node.
In regards to the HDD overselling, sure you can do it manually that way, but SolusVM doesn't support doing that via the GUI, i guess i should have been more clear.