Pro's – Solaris/Sun have big footprint in big data centers running big Oracle app's. Big Oracle shops spend big money and buy big stuff. Solaris works, and big Sparc's work so the only real reason to run away from that is Intel/Linux but that movement seems weak in this specific arena. Thus, Sun remaining viable has an install base that is absolutely valuable – shrinking, but valuable.
Solaris is enterprise critical, but so was VMS. I'm not sure that no matter how great it is, anyone would continue to push it in the face of the Linux realities. Sparc? Probably not. Most systems they ship are already x86 now, so I can't imagine continued development expense gets sunk into Sparc. If IBM is serious, however, they have proven they can take a corner case architecture and make a lot of money on it for a long time – i.e. the Mainframe and AS400. I don't see this being the same game, but it does show that they can do stuff like this when it makes sense. If there is enough money in it, they can wait out the whole market until it becomes a monopoly.
What's left of STK means IBM owns the entire market for high-end tape.
IGS should find itself a lot of new opportunities inside that base.
Con's – It seems expensive, and most likely will only get cheaper. Sun has been progressing nowhere but down over the last half decade and forces are not moving in their favor. It would require someone like IBM to be able to recoup that kind of investment in that size customer base. It will be a lot of work for IBM to quickly identify and get to the customer base less those customers who aren't hip to the IBM play will most likely accellerate their plans to run away.
Other – this could all be total bullsh&t. I've started rumors bigger than this one.






IBM buying Sun is sooo last century. With Sun out of gas, who cares if IBM buys the company or it "winds down" like DEC. Doesn't IBM have something innovative to do with all that money - like Apple and Google have? Read more at http://www.ThePhoenixPrinciple.com