MySQL has a reputation of being a lightweight database. This definition can be intended either as having limited features or as requiring little hardware.
In my experience, I have seen MySQL used in quite heavy load situations, and thus I will discard the first meaning of lightweight. As for expensive hardware, my own experience is mixed. Yahoo! and Google have shown the world that using an array of inexpensive boxes in replication is often the most sensible way of scaling. However, there are many users who don't feel comfortable with replication, and therefore buy more iron when their current box has reached its limits. Sometimes, an upgrade could be avoided by proper configuration, but this is beyond the point. Given the choice, what is your favorite hardware for MySQL?
There is a quick poll on the Dev Zone asking this question.
My own prediction is that we'll get an overwhelming majority of x86 1CPU-Dual core, but this is just a wild guess. Do you use anything different? Please, prove me wrong! Are you on my assumed majority slice? Then prove me right!
If you don't care about what I think (and you shouldn't, really!) please cast a vote for your favorite architecture!