I have a problem with KMPlayer:
I use KMPlayer to stream radio stations from my home computer's TV card to my N900.
This all works fine, but whenever I lock/unlock the screen the stream stops.
If I leave the phone alone to go dim the screen by itself there is no problem, but ıf I unlock or manually lock the screen this happens.

Odd, I just tested this with a radio stream (radioparadise) and, except from a small hickup, it just kept on playling. Used the default player (gstreamer aka osso-media-server). I know that mplayer outputs after these hick-ups caused by the screen dimming, 'trying to reset alsa'. Are you using mplayer?
Btw. can you reproduce this with a internet radio stream? If yes, can you post the link you were using?

Update: last week I had this strange effect that when leaving my apartment, listening to a mp3, the sound notification of the terminating wifi connection, caused the playback to stop. I had to press the stop button and play button to get it going again. A reboot solved this.

I am indeed using MPlayer as backend.
http://superfmaac.radyolarburada.com:9235/
I seem to have the same problem, but less frequently on this stream.
This made me think that maybe the AAC/MP4 codec is a bit heavy since my home pc streams in that format too. I will try different formats and report back with my results.

My reports are as follows:
128Kbit and 256Kbit MPEG4:
takes a long while to buffer and play.
Stops playing when the screen is locked / unlocked. Will play again if stopped and played.
256Kbit MP3:
Buffers faster than AAC and stutters heavily when doing other stuff. Will stop playing after a few unlocks.
128Kbit mp3:
Same buffer speed. Doesn't stutter as much when doing other stuff. Playback stops occasionally.

gstreamer plays this stream just fine for me (I have decoder support installed, don't know if that is needed for this stream).

Anyhow, before next release I experiment with mplayer and pulse audio output driver again. This was broken some time ago and therefore, mplayer uses alsa currently.

Yes osso plays it fine.
My problem is that OSSO doesn't play streams muxed in TS / PS / ASF or OGG and therefore I'm unable to use osso for my home PC's video/audio streaming

Build kmplayer_0.10.3.901-1 for you that sets audio output driver for MPlayer to pulse. It's in extras-testing. The bug I saw before apparently is fixed in MPlayer (was that the volume was 100% when MPlayer started playing)
Can you try this one?

Oh oh ! It works!
Thank you SO much for this new version
The buffering is also WAY faster now. Before it took like 40 seconds now it takes like 5 on 256Kbit MPEG4 audio.

Cool Lets keep it so then.