I first heard about the idea of tainted /8 blocks from Tony Hain from Cisco a few years ago (thanks for sharing your ideas). The fear was that some IPv4 addresses were unusable because some equipment vendors, documents and networks would use addresses from those blocks “illegally”.
One of the most tainted block could be the 1/8 block (Come on, who hasn’t used 220.127.116.11 or 18.104.22.168 in an example in documentation or as an IPv4 for a quick hack). One excellent description of the problem and a study on how tainted those blocks could be can be found in Mark Blachets blog.
Thankfully the problem does not appear to be as severe as initially anticipated. APNIC got the 1/8 block allocated from IANA in January 2010 and started to delegated large chunks of the block in May of 2010 as described here
There are reports about some bogus traffic to a few of the addresses within the 1/8 block. What has happened is that APNIC reserved and trashed a few /24 from the 1/8 block.. Those /24 will probably never be used on the Internet. These blocks in question are 22.214.171.124/24, 126.96.36.199/24, 188.8.131.52/24, 184.108.40.206/24, 220.127.116.11/24 that totaling about 1000 addresses. A whois lookup points them to researchers at APNIC. Most of the rest of the block is now allocated to various APNIC members.
RIPE allocated the 2/8 block from IANA in September 2009. Most of the addresses are used up, for example 18.104.22.168 is delegated to France Telecom. There are no signs of small delegations that are thrown away because of dirtyness in the 2/8 block.
The conclusion that can be drawn is that we do not have to be overly concerned about tainted IPv4 addresses. The problem appears to only affect very specific subnets and IPv4 addresses and not whole /8. I would assume that the same will be seen in other potentially tainted blocks such as 100/8.