Only to practice on.
In my view, Solaris on SPARC is a great choice because the integration of hardware and software is so complete and because it's so well supported by software vendors. You can partly mitigate the former by buying an x64 server from Oracle, but there's nothing you can do about the generally poor level of vendor enthusiasm for Solaris on Intel.
My advice is that if you really want a Unix-like OS to run on cheap commodity hardware, go for Red Hat (or even SuSE). Otherwise pay up and get the SPARC boxes in.