Running cvs HEAD I now realize that I grew to rely on checking the modeline of lisp buffers to see whether there are outstanding requests. Often, I start evalutations that take minutes or hours to finish and it's useful to have this at a glance without having to worry about missing when the return value is printed or having to check the running threads.
The attached patch does not reinstate "eval...", instead it displays the number of outstanding requests like "CON:sbcl{3}" if it's greater than zero.
Currently there is a loop through buffer-list, it that's a problem maybe there is a better way to arrange for the modeline to be updated using a global mode-line-format variable as a trigger to signal the change in connection-state that is to be recomputed in each slime buffer.
The patch does not solve the minor problems caused by the use of run-with-idle-timer, namely that the modeline may not be updated if the status of the connection changes in the background while emacs is idle.
Cheers, Gábor