Even if you assume all the traffic comes in during just an 8 hour window of a 24 hour day, that's still barely over 1TPS. It's nothing. You didn't say how big your dataset was in mysql. If you were at 100x data to RAM ratio I would definitely be worried, or if you had any especially slow queries. I think even if you were at 10x data to RAM ratio you would be okay mysql-wise, assuming you're getting something close to 10ms latency on your disks. (Which you ought to be able to with Linode/Slicehost/EC2). If your app for whatever reason has burstiness (e.g. sharing/viral events) then you need to plan around whatever peak load you're willing to support.
BTW, my personal opinion is that Joyent is grossly grossly overpriced. And are they still forcing you to run Solaris?
BTW, my personal opinion is that Joyent is grossly grossly overpriced. And are they still forcing you to run Solaris?