wheel - 11:54 am on Sep 28, 2011 (gmt 0)
Yes, this is worrying on servers. My linux server does the same thing. PC folks are used to having lots of memory available, and running out is a bad thing. Servers, as robzilla points out, are different.
I would check CPU load as well - that's likely to be much more telling about what's going on on the server. You do want lots of CPU load available. Mine runs at a few percentage points of capacity - much higher than that and I'd start getting concerned.