I put in 2 types of alerts, one for a general topic of interest, (Robert Falcon Scott Terra Nova - I'm very interested in Antarctic exploration and Scott's last expedition in particular) and 2 for more specific things, "New Zealand String Quartet" and "Raukatauri Music Therapy Centre" which are both groups I'm interested in (a friend of mine is therapist at the centre). Over the last few days I've had a steady list of alerts popping up on the email. The specific searches using phrasing marks did seem to provide better hits, and I didn't get any duplicates. Again, playing round with your search strategies until you get the results you want is the way to go.
Google Alerts seems a very useful way of keeping abreast of information and mention of topics of interest on the Internet in a convenient way, as unlike with Bloglines and so on, it doesn't require logging in to a separate site, but is delivered straight to your email. From there you go straight into the link or not as you wish, and it works in the same way as a saved search on the remote databases, so that you don't have to repeat the search every time. However, with RSS feeds it is always from the same source, whereas with Google Alerts the information could be from anywhere and not necessarily always with the same relevance.
This service would be useful for patrons to know about if they have a regular requirement for certain information or wanted to follow a topic or whatever. It is another thing which people can choose to use or not depending on what their needs and interests are, but knowing about it and having the choice is the crucial thing. The Internet is pretty huge and amorphous, so anything which helps people navigate and use it more effectively is welcome.