I don't think the Solaris license is too restrictive at all, but I never got
into all that stuff. I use ZFS on two 4 year old Dell Precision 450 with dual
2.26 Ghz P4 and 2GB of RAM
and it performs very well.
Solaris 10 driver support is obviously not as good as Linux, but I think it's
real close these days. It is very good if you are using SCSI or SAS, less so
for SATA, although if you select legacy mode if the SATA contoller isn't
supported then it would install fine. I always stick to SCSI or SAS anyway. If
you are buying new machines Sun's AMD x64 servers and workstations have very
good EDU pricing and are competitive. IBM is now selling servers with Solaris
pre-installed and certified. The Solaris 10 HCL is here:
http://www.sun.com/bigadmin/hcl for components or whole systems.
If you were to install it on a workstation I recommend getting an nVidia video
card since they make their own Solaris driver which is very. very good (closed
source I think, but very, very good).