I had a SH DC594, and would completely agree with Steve's take. Fantastic gutiar.I have a DC 594 SH. It is a great guitar. The SH aspect makes it a bit lighter and provides a bit more "resonance" or "warmth", maybe?
I also lust after a SC 594 SH, so that may tell you how much I like it.
I bought a 594 semi hollow a few years back and absolutely love it. It was a special run for somebody, can't remember who.
I also have HB-IIs and McCarty solidbodies, and this falls somewhere in between. It's also my first guitar with the 58/15 LT pickups and that Pattern Vintage neck, both of which I love. The guitar rings like a bell and has enormous chime and presence, as well as freakish sustain. It's a keeper - even within the menagerie of my other PRS guitars.
Gratuitous pics, because, well, that's why we're all here: (from original seller)
In my experience, PRS Semi-Hollows are more like 'weight-relief' than having a more 'noticeable' impact on the tone as we associate with other Semi-hollows - like a 335. I think its because of the very different build style as a PRS Semi-Hollow is made more like a Solid body but with a bigger chamber. Most semi-hollows are made from a thin Laminated back, top and sides and often have a 'larger' body too so have more room and thinner bodies for them to resonate more. The cavity isn't that 'deep' - the guitars are not thick and you don't want the back and sides too thin with their grain structure (made out of a Slab of wood as opposed to Laminates with opposing grain structure to add strength) so it acts more like weight relief.
This is my Semi-Hollow - a Limited Edition Special Semi-Hollow.
I also have two PRS Hollowbodies (594 (my pfp) & HBii with Piezo) and these have more of that airyness and warmth you associate with a 335.
As for any 'cons' to owning a PRS Semi-Hollow, I can't think of ANY that any 'normal' usage would impact. If you want to stand on your guitar or chuck it around, its not going to take as much abuse because its not 'solid' but its not like some semi-hollows where 'feedback' can be an issue on stage. In fact, even the PRS Hollowbody is very manageable too.
I would certainly consider swapping my 'solid' body PRS guitars for a Semi-hollow version if only for the weight saving - although I must admit, I do think the F-Holes make a guitar look 'classy' too. The only 'con' to not buying a PRS semi-hollow as far as I am concerned is that extra weight you'll have to carry - not that PRS guitars are generally 'heavy' (over 10lbs) but you can save around a pound or so in weight by buying a Semi-hollow.