Our little bio-informatics group got rid of our Windows installs and got Debian last year (2003). We now have several desktops running Debian (which are also test-environments for the development of several large and tens of smaller web-based applications) and one small server. We have plans to migrate our other Linux servers to Debian (many running Sun Solaris now) and are in the process of getting a new Sun server which will be running Debian as well. We mainly use Apache, PHP, MySQL, Exim, Samba, SSH and (S)FTP on our servers together with some CPU intensive programs for the researchers in our department.
We chose Linux for stability and a better environment for our applications, and we chose Debian over others mainly because of apt. Never seen installing a new kernel that easy...