The paradigm has shifted quite a bit since the hey-day of AIX systems.  Back 
then, you would custom configure a substantial AIX system, and require premium 
service from IBM, with fast response from them.  RS/6000s were renowned for 
reliability, though, with very few core system problems (most problems 
happening in costly adapter cards).  With "commodity" type Intel hardware, 
reliability is acceptably "okay", DoAs not uncommon, and redundancy realistic 
in the form of adjoining rack mount X-series or similar boxes, or even blades.  
Most software products have accommodated the paradigm shift, and are sold for 
Linux as well now.

The major challenge these days is not computer cost but the cost of supporting 
complexity, as many companies are finding out the hard way.  Disk arrays with 
multi-level RAID, SANs, and VMs make for an amalgam that is becoming impossible 
for humans to understand.  Downtimes and service-level problems are a big 
factor in implementations.  (Ugh - a RAID array is rebuilding and will entail 
hours of impaired performance... Sure hope another disk doesn't fail before 
that completes or we may lose everything.)  And good luck getting vendor 
support: they will know their little piece, but recoil if you try to involve 
them in the larger picture.  This is making for a substantial market for 
technology consultants, who may be your only hope of dealing with the 
complexity; and that adds substantial cost to implementations.

Oh, the days of simple computer systems...

    Richard Sims