Sorry, but I need custom data fields for user registration and to be able to use them pretty much arbitrarily for selection of who to send messages to. The announcement list doesn't seem to even come near my client's needs.
On the other hand, could you define throttling some more? I specifically asked support about this and got a completely unsatisfactory response, basically, "We suggest you use the announcement lists, and if you bog the server, we'll just shut your script down." I don't believe there aren't some actual numbers attached to this.
PHPList is highly configurable, and it'd be easy to keep it within any limits you may have. At the moment, for example, I've got my client's installation sending out bursts of 50 messages each spaced two seconds apart, with 90 seconds between bursts.
I'm still having the issue of the send dying, which suggests it's a software problem, but it'd still be nice to not be poking around in the dark wondering if I'm causing a server issue at the same time as trying to figure out if it's really a software issue.