You'll be using pkgadd instead of apt?
You're not going to run into any huge gotchas. If anything, you may have a better experience, seeing how much of what you're installing is Sun software (apparently, all of it).
The problems you can have with proprietary Unix are most notable when you move outside the proprietary comfort zone. If you like non-mainstream OSS, you're going to have to learn to love to compile from source, because Solaris binaries may not be available. Otherwise, what? Different gui?
Sun hardware is solid and elegant. Support is responsive like you can't even imagine if you're used to Dell, et al. Solaris is stable and exhaustively tested. Imho, it's not worth the price for anything but a critical application, but if you've got it, it's very enjoyable.