I found in my apache log 2 errors, causing the RSS-feeds very slow to load (avoiding display of page)
-PHP Notice: undefined property:MagpieRSS::$etag in /../rss_fetch.inc on line 158
-PHP Notice: Undefined index: description in /.../rss_client/block_rss_client.php on line 223
The installation runs on latest mysql5, php5 and Apache2
This error occurs on that machine in 1.5 and 1.6
Not always, probably only when the RSS feed is renewed.