You may have heard of this elsewhere. This is a Grey Hat report from a anonymous individual, that has used a botnet to survey the entire IPV4 address space and perform a port scan on every one of those IP addresses.
In summary he delivered his scanning software to 30 thousand machines that provided a telnet port (23) that accepted a logon of either root/root root/(blank) admin/admin admin/(blank) or even (blank)/(blank). There were many more of these devices, but this was sufficient to his requirement to scan the entire IPv4 range in about 3 hours.
The main implication from this is the availability of these hosts could be used for DDoS and other botnet activities. One would speculate that they may be an increase in this type of activity going forward.