When will the US-IV processor start appearing in workstations like
Blade 2500, etc.?

Is the US-IV pin compatible with the US-IIIi (I believe it is
with the US-III) and will one be able to swap a US-IV CPU into a
Sun Fire V250 (US-IIIi)?

The naming convention for these products is horrible (US-III, IIIi,
and now these Opteron machines with the w's and z's, 20 vs. 200)
and doesn't get better ...