Here's a list of some SKS' features:
Highly efficient and reliable reconciliation algorithm
Follows RFC2440 and RFC2440bis carefully --- unlike PKS, SKS supports new and old style packets, photoID packets, multiple subkeys, and pretty much everything allowed by the RFCs.
Fully compatible with PKS system --- can both send and receive syncs from PKS servers, ensuring seamless connectivity.
Simple configuration: each host just needs a (partial) list of the other participating key servers. Gossip is used to distribute information without putting a heavy load an any one host.
Supports HKP/web-based querying, and soon-to-be-standard machine readable indices
The design of SKS is deliberately simple. The server consists of two single-threaded processes. The first, "sks db", fulfills the normal jobs associated with a public key server, such as answering web requests. The only special functionality of "sks db" is that it keeps a log summarizing the changes to the key database. "sks recon" does all the work with respect to reconciling hosts databases. "sks recon" keeps track of specialized summary information about the database, and can use that information to efficiently determine the differences between its database and that of another host.