As long as you don't have to worry about endian stuff, the code is exactly the same for Solaris x86 as for Sparc.
Going between Solaris and Linux is a much larger effort (I've done this before).
The key with Solaris x86 is that there are some Solaris admins out there who realize that Sparc hardware is slower for a lot of things, but they don't want to deal with Linux to get the speed gains. Things like commodity web servers, etc., are great targets for Solaris x86 in an all-Solaris shop. Keep the database on the big many-CPU iron, and put the load balanced smaller stuff on cheap fast machines.