I used phplist at another host. I found it very helpful for managing emails to people who attended my classes. I maintained a handful of lists to which they could subscribe/unsubscribe. I never got over 500 users, but it was easy to send emails to one or all of my lists.
Now I have just moved my site to dreamhost, and I need to decide whether to install phplist here or just migrate to Dreamhost's announcement list. I'd appreciate insights from any one who's made either or both moves.