Another related application of digital signatures in a web environment could be to send (possibly encrypted) and digitally signed session state information to the client web browser in order to offload session management overhead. Obviously, the digital signature process adds overhead in terms of extra processing and complexity, but the upside is that the server does not have to maintain state for each client connection.

E.g. for a web site having a shopping cart (i.e. list of items selected for purchase), encrypting and digitally signing the shopping cart and send it to the web client means that the web server does not have to keep track of who's buying what. When the person in front of the computer decides to go to checkout, the whole shopping cart is sent back to the web server, verified and decrypted.

The subject was discussed here (Security Now podcast, Episode 110).