Is Servermojo useful to monitor server/website uptime?

I haven't heard of ServerMojo before however it looks like their offer is pretty basic to fit the needs as to what you are looking for.

I have 2 additional recommendations I would feel are worth mentioning. Pingdom - www.pingdom.com; great client base and mobile utilities. & For all of the bells and whistles, without a doubt Gomez www.gomez.com

Most hosting providers offer this service as complimentary for doing business with them if that is where your servers are although I would agree 2 or more helps especially external facing customer responses times.

Servermojo looks like a good standard monitoring service. As Nick said, many hosting providers also offer this service.

If you have a more complex website (like we do) I would recommend one of the newer services that allow you monitor/test your site in a real web browser.

We run test macros in Internet Explorer and Firefox every 15 min that test the complete sequence of product search, selection, checkout and credit card payment.

We use AlertFox, and their support has been great. They also have a useful free monitoring option, which is a bit hidden on their plans page. The free version gives you one real browser test (and three normal ones).

The keyword here is "real browser monitoring". If you google for that you will find a few other options as well.