I'm anticipating very few customers with very many recurrence rules.
Well in that case why bother? It hardly matters what approach you take if you're not planning for lots of users. Surely your server has the power to compute tons of calender data for just a few users.
Heh ... I didn't mean the system would have very few customers: I meant many customers, but only a few with a *lot* of recurrence rules (i.e. enough to be a burden to a minimally-configured client).
You're probably right. It's getting difficult to *not* have a beefy server any longer.