I'm getting the warning below. I tried to chmod wp-content/multi-feed-reader/ to give group write permissions. But the error still appears.
Warning: .../wp-content/multi-feed-reader/cache/...bb.spc is not writeable in .../wp-includes/class-simplepie.php on line 1780
The error might appear only the first time a new feed is added. Haven't confirmed this yet.
I'm running this on one blog of a multisite install with wp-supercache running. I don't thing that would cause trouble, but posting it here just in case.
By the way -- this plugin is really amazing. Simple to use, but really powerful.