Have an SBS2011 running Exchange, a database app and a few other things serving 5 users (3 low use, 1 high).
The server was never specced for the database app so it isn't as powerful as I'd like... Only 12GB RAM.
We have increasingly found performance problems with this server, last week it was so bad I couldn't even connect remotely.
To free up some available RAM I have (over the past month or so):
Restricted the Exchange Message Store to 1GB with (so far) no ill effects.
Now I am finding that IIS Worker threads are using up the available memory and I have (so far) been unable to track down much useful information about restricting them.
This server is not 'serving' anything web-based apart from OWA that I am finding people using because Outlook is so slow (again related to the Servers performance).
I am aware that Exchange on SBS2011 is designed to use up available resources (and concede when other applications request). But it is not doing so (or anywhere near fast enough) for our needs.
Opening the database application (using Postgres) takes 5+ minutes from client machines and regularly times out or crashes due to this.
After a reboot (before SQL/Exchange/IIS databases are very large/totally cached) we get the performace we need and expect. Previously a reboot once a month was enough... Then once a week... Now they have taken to rebooting it almost daily!