Waasup with all of the users named "Yahoo! Slurp Spider" showing on the "Who's Online" Pages. Earlier there was also an "AskJeeves Slurp Spider" user shown. Note that these user names do not appear as active links like a registered user name would. IS the site under attack?

Nope! It's web indexing by Yahoo -- the "Slurp spider" (their name) collects documents on the Web to build a searchable index for services using Yahoo. The documents are discovered and crawled due to other web sites having links to them.