1) If the workspace is open in Eclipse, I can't use scm:

C:\UserData\sedlock\rtc\workspace01\comp3>scm status
Could not initialize data area:
Another RCP application is running in this local workspace. File locked at file:C:\UserData\sedlock\rtc\workspace01

This is not good.

2) scm.exe seems to work fine in cygwin, except for the status command, which returns nothing:

************
sedlock@mucn13423 /cygdrive/c/UserData/sedlock/rtc/workspace01/comp3
$ scm.exe status

sedlock@mucn13423 /cygdrive/c/UserData/sedlock/rtc/workspace01/comp3
************

3) The doc says that if I login first, I should not be prompted for credentials, but I am always prompted for password.

C:\UserData\sedlock\rtc\workspace02>scm status
Password (sedlock @ https://localhost:9443/jazz/):

I can only use scm comfortably by supplying the password with -P.

4) There seems to be about a 20 second delay before anything happens after invoking scm. This is obviously a serious obstacle to using it in scripts where you may want to invoke it several times or in a loop.

I was going to benchmark RTC checkin vs. CC checkin with a loop that checks in files individually, which is perfectly fine with cleartool, when I realized that RTC was going to perform far worse than CC. I changed the script to check in the files in one go, and found that RTC checkin is, in my setup, about 3 times faster. But it is not always feasible to batch invocations of scm together.

I guess the overhead is the server login. I think you've got to implement some way of saving state so that invocations of scm within one login session do not require new server logins, but start to do their job immediately.