Summary
I see probes as being useful in small to medium-sized Domino networks. Up to ten servers would be appropriate. The price is also ideal. It's free! Environments larger than ten servers are more complex and can probably justify the cost of a more elaborate monitoring solution.

When you have two servers in your Domino network, you can configure both servers to probe each other to ensure that they are both up and available. When you have more than two to monitor, a good solution would be a dedicated PC-class machine that runs a copy of Domino and does nothing but monitor the other servers.

Don't forget that the TCP probes can also be used to monitor any servers in your network that provide these standard Internet services: DNS, FTP, HTTP, IMAP, LDAP, NNTP, POP3, or SMTP. It doesn't need to be a Domino server that's being probed.

I hope that this convinces you to have a deeper look at this feature, if you haven't already. Also, check out whether this can be of use in helping you better manage your Domino network. Now and go and have some fun!

Greg Neilson is a Senior Notes Architect at a large IT services firm in Australia. He is the author of the forthcoming book "Lotus Domino in a Nutshell" for O'Reilly. You can find out more information about the book at http://www.oreilly.com/catalog/domino.