Last week someone asked me if the DITL 2009 data could shed any light on the amount of queries sent to TLDs with wildcards. While we do have data from a few TLD operators, it wouldn't really help to answer this question. However, I think we can get a "first-order approximation" by looking at the queries to root nameservers. Note that by looking at queries to the roots, we have no knowledge of client queries that are cache hits and those that are sent to the TLD nameservers due to cached referrals. We could perhaps turn to a passive DNS collection, such as SIE for a second opinion.
The long, tall graph below shows the query rate to each TLD seen in the DITL 2009 data. Those TLDs known to have wildcards are shown in blue. Note, however, that some TLDs (such as CN and KR) implement wildcards only for IDN names.