Some time ago, I installed RHL 5.1 for SPARC on a spare 535Mb hard drive in the SS5 I normally use at work. (If my colleagues are reading this, then that hard drive is definitely not spare so keep your filthy hands off it!) Occasionally, I booted it up for a play and then went back to Solaris 2.6 on the other disk when I found something I needed under that OS that my Linux installation didn't have (e.g. native Netscape, sound support).
Recently, I decided to make a serious attempt at migrating to Linux permanently. Why? Um, because I felt like a change. Because Linux was clearly where it's at (OK, so I believed the hype too). Because Solaris 2.6 doesn't run as fast on a SS5 as 2.5.1 used to, and Solaris 7 will probably perform worse again, whereas Linux is small enough to cope better on a client desktop. (On an Enterprise 4500 however, I can assure you it will be a different story; this is really the market Sun are targetting now.) And because it might be a better environment.
On a practical basis, my company is on the verge of releasing a Linux port of its high availability product. Since this product is closely tied to the operating system environment and I am involved with product packaging and support, it makes sense to gain a working knowledge of Linux. I need at least as much as our average customer.
I admit that the one thing that made this swap a viable proposition was Netscape's release of a Navigator 4.5 S/Linux port. That really was the one piece I was missing. Unfortunately, it turned out to have its own set of problems, as I will cover shortly.