We are getting a problem querying chatter feeds in Apex.  At sporadic times we get an error page:-

"Unable to Process Request

Concurrent requests limit exceeded.

To protect all customers from excessive usage and Denial of Service attacks, we limit the number of long-running requests that are processed at the same time by an organization. Your request has been denied because this limit has been exceeded by your organization. Please try your request again later.".

If we take out the query to NewsFeed or Object__Feed then it all works fine.  With those queries we get the sporadic error.  Once the error appears then all subseqent queries to NewsFeed fail for about 30 minutes.  After that the queries start working again.

Note that we are not using any Webservice or API calls etc.  The queries are in vanilla Visualforce controllers in Apex.  No Ajax callback or anything like that.   The error happens whether or not we use Eclipse to develop.

We only first noticed this since summer 10 went live, but that could be a coincidence as the app is being actively developed.

Anyone else have this problem?  Even better, a cure?  Or is this an SFDC bug?