The short answer: In many cases, no.
Because our infrastructure does not manage resources at a fine grain, anyone with a CS account can login to the cycle servers, access the file system (including world-readable files), create a web page, send email through our systems, request a database, manage a mailing list, and more.
For this reason, each new account represents (1) an incremental security risk to all of the current users and (2) an additional consumer of the department's resources. This is why we'll often reply to a request for an account with, "why is this account needed?"
Recognizing the need for collaboration, csstaff has, over time, rolled out new capabilities that can often eliminate the need for additional guest accounts. These include such services as incoming and outgoing FTP, and an RSYNC service for data sharing. In addition, current users are able to install web applications such as blogs or wikis within their web space. These applications maintain their own user "accounts" that are only used within the application.
So, before requesting a guest account, please take a moment to determine what capabilities the guest really needs. It's likely that we can grant these capabilities without the need for a full-blown account