I rather like the idea of co-location for mac minis. It seems like a really cost-effective choice for a lot of applications. Essentially, if you want a lot of memory, and disk and cpu, and don't need vast bandwidth, then Mac Mini co-location could be a really low cost option.
Good applications for this sort of hosting would be departmental applications, websites like eastagile.com, or even advanced analytic and data applications that are stable in terms of size. We do not use Mac Mini hosting, but the idea is intriguing for such applications.
This is not for everyone. If you need massive bandwidth and a highly flexible infrastructure, with lesser needs for cpu and disk then Joyent, Engine Yard or Amazon EC2 are better options. And Joyent and Engine Yard have impressive expertise in Ruby on Rails. For that reason, most of our hosts have opted for this direction.
Mac Mini Co-location
A mac mini server
8 GB of RAM
2 500 GB Hard drives (1 TB)
2.53 Ghz Intel Core 2 Duo
Lots of external hard drive space for backups and files to serve
(plus, I bet for less than $200/month you could convince them to host an $800 Promise SmartStor DS4600 for 4TB of external firewire 800 RAID).
The hardware costs about $1,650 (mini + 1 TB external drive) and they will set it up for you. Add the $840 in annual hosting costs, and $2,490 or so will cover hardware purchase and hosting for a year. The real cost is lower since you can probably expect to get more than a year of use out of the server. One might argue that these Macs are not the most reliable machines on the market, or other options are more dependable. But at these prices, it might make sense if you can consider purchasing more redundant machines than you could otherwise. If you want redundancy, you could host at two different mac mini hosting facilities, such as xservhosting and macminicolo.
Bandwidth included is 200GB/month and $1.75GB beyond that.
I haven't asked exactly how it would work, but it seems to me that a special benefit of mac mini hosting is that one can just easily have the server put in a FedEx package and mailed to you. It is small enough that this seems easy to manage.
Remember, of course, that you need to handle the infrastructure and all that stuff yourself. That can be a big deal, or not.
Now lets compare this to other hosting options.
These guys are good. We have used them for years and host eastagile.com
on them. But they are so expensive we are careful to use only barely adequately powered machines. It is almost like mainframe days again.
8 GB Joyent virtual machine with 2 cpu cores (burstable to 7 cores) and 100 GB of storage. $1,000/month, $12,000/year.
1TB of storage costs $1,500/year. This is NAS (network storage) which is slow, but presumably highly redundant.
$0.15/GB for extra bandwidth after first 10 TB. Note that is is immensely cheaper, and more, than the mac mini colocation providers.