centos - Is this a good behaviour?

My centos 5.7 is running Magento.
4GB RAM and 4 Cores.
Nginx + spwan-fcgi + memcached (Best performance if you ask me).

Now i'm a little bit concerned about the Memory usage.

[root@adikastyle shipment]# free -m
             total       used       free     shared    buffers     cached

Mem:          3948       3712        236          0        224       **2377**
-/+ buffers/cache:       1109       2839
Swap:        10975          0      10975

I've seen in few forum's this command:

# sync; echo 3 > /proc/sys/vm/drop_caches

the website is fast and handle many cur-connections.

but the cache is really strange..

1. Is this command is safe for production?




2. Does the 2377MB of cache is good ?




3. Do i have to change something?

Thanks.