Here's a list of topics in #bitcoin-wizards since 2014-02-23 that have elicited a "check the logs" response.

multi-party computation
timelock proof-of-work
timelock puzzles
timelock encryption
decentralized coinjoin system using blind signatures
2-way peg
double-spend hash tree proof
why is it difficult to make bitcoin anonymous
data structures where everyone only needs to explicitly store the parts that contain their own coins
problems with maidsafe/storj
proof-of-funds scheme could be replaced by a zero-knowledge proof
follow users cross-network by intersecting their filters
creating auditing motivations for off-chain systems
problems with proof-of-stake
"just know all the competing histories" (re: proof-of-stake)
moxie
lightning network
birthday problem
merkle mountain range
fake histories
hashimoto
incorporating pooled mining directly into the protocol
ways to create commitments