we're working on the server a lot, see this:
https://wiki.unsystem.net/en/index.php/Libbitcoin/Blockchain/htdb_slab_Performance

here are the development repos:
https://github.com/libbitcoin/libbitcoin-explorer (formerly sx)
https://github.com/libbitcoin/libbitcoin-server (formerly Obelisk)

sx has basically been rewritten by eric voskuil, and the server will undergo more improvements too (see https://github.com/libbitcoin/libbitcoin-protocol ) which will allow SPV for wallets with the new protocol.