I have seen this reported in the forums but don't see the issue in the issue tracker. The problem is VERY slow performance for document library sizes that have any size. The performance is acceptable for admins and community admins, but extremely slow for non-admins (or non-community admins). One user reported, through his analysis, that the reason was a large number of queries that happen. See his information below in quotes:
"It takes about 15 seconds to load when Organization Administrator click the Document Tab to load the Document Library Portlet. But it takes almost 3 minutes to load when Organization Member do the same action. During the page load, the mySQL consumes all the CPU power on the server. Then, I enable the query log on mySQL server to log down all SQL statement and found that the number of SQL statements the Organization Administrator will do is A LOT less than around 30 compare to Organization Member of 1500 SQL statements."
I have been using Liferay 5.2.3 successfully with around 1300 files, 800 folders, 180 MB. It works fairly quickly in Liferay 5.2.3 but is very slow on initial load for non-admins. This is true both for the document library portlet and the display portlet. It causes the full page load to be degraded since presumably it is doing all of these queries before initial display.
We utilize this also fairly extensively and switched over to Liferay 6 already for production. I didn't notice this until after the upgrade when logged on as another user.
The load time is prohibitively slow, so this needs to be a high priority. In timing it today, it took 1 minute and 20 seconds before the page displayed with the library portlet. It is worse because it looks like, in IE, the page is done loading but it finally just comes up eventually. Browser type doesn't have an impact.