Generally speaking, you should be pretty darn safe querying production systems using SNMP, as long as you only 'get' using the read-only community string, and avoid 'set'ting anything using read-write or read-write-all community string.   I suppose that if you tried really hard, you might be able to crash your access router, but I'm happily cluefree on possible details.

If you want a head start with your SNMP perlings, there are several working examples in the Networking Code section of Code Catacombs.   I'm reasonably happy with some of my own code there: "(code) Net::SNMP, Bandwidth, GnuPlot, PNG, PostScript, Excel" and "(code) Net::SNMP, table-ish interface stats" plus "Cisco SNMP CDP Poll" as well as "(code) mind your snmPs & Qs".
    cheers,
    Don
    striving toward Perl Adept
    (it's pronounced "why-bick")

Update: here's a few URLs that may be of interest:

• http://www.telecomm.uh.edu/stats/rfc/
• http://www.alvestrand.no/objectid/
• http://www.ibr.cs.tu-bs.de/cgi-bin/sbrowser.cgi
• http://net-snmp.sourceforge.net/
• http://www.cisco.com/warp/public/477/SNMP/snmp-indx.html
• ftp://ftp.cisco.com/pub/mibs/supportlists/