I would not buy a Fantom. I owned one and it went back to the store shortly thereafter. Since you're dangerously close to buying it I'll go into some detail to try and talk you out of it.
It is sort of a 'jack-of-all-trades' type of box, but of course master of none. However it depends what you want it for, and what type of sounds and programming abilities you're going for. In my case and opinion, I was looking for two things: 1. Really realistic sounds for standard instruments and drums 2. Really way out there sounds and sampling morphing mangling capability.
The Roland Fantom as mentioned here by others has a mediocre sound set when it comes to standard sounds such as pianos, sax, drums, organs, cellos, flutes, etc. etc. The Motif ES series absolutely smokes it when it comes to these sound sets. The level of realism is above and beyond in the Motif series.
Now yes the Fantom does come with sampling and sequencing capabilities, but again if you're using a DAW for sequencing it becomes useless, and the sampling is very limited. On the plus side the Fantom interface is better than the Motif with the color screen, and it comes with digital out and balanced outs standard, and on the Motif you need to spend a few hundred extra to get the digital in/out board, etc.
What I ended up doing is returning the Fantom and getting a Motif ES Rack for all my traditional sounds (stunning sounds in this IMO and the rack does have the SPDIF out standard), and a Roland V-Synth XT Rack for all the progammable synth and sampling related stuff, since the capabilities of the V-Synth XT runs circles around the Fantom in this department, and there's no code/space wasted trying to come up with the next bestest awesome grand piano sound. The V-Synth also offers editing far and above the Fantom's capabilities.
Again, they tried to stuff pieces and parts of everything into the Fantom but IMO it doesn't fly. The only reason to get the Fantom would be if you're a keyboard player by background who is used to programming on a keyboard and are out performing and at rehearsals, etc. where you need the keyboard/sequencing/recording/sampling/diverse sound set all in one neat package and can afford to have limits on each of those aspects.
Before I got the Fantom I thought it would be the answer to everything but I'm much happier now with the Motif ES Rack, and I'm waiting for the V-Synth XT to arrive from Roland. My friend knows the Roland rep and they have sold out of V-Synth XT's in this country (at distributor level) since the demand has been so high. Supposedly the boat just came in on the West Coast from Japan with a pile of XT's so I should have it within about a week.
It's been reviewed highly in every pub that's reviewed it (and it seems like every pub has reviewed it in the last two months) and you should go to the Roland site
www.rolandus.com and watch through every video demo of the V-Synth XT and you will understand the sheer creative power of this thing when it comes to editing, programming, and sound mangling. The plug-in expansion boards they're coming out with for this are awesome as well, and it comes with two already installed.
One other note on the Motif's - the arpeggio's are awesome. Motif's come with 1,800 arpgeggios's, Fantoms come with 128. Do the math on how much this expands the creative possibilities of the respective sound sets. The only limit is on the rack version Motif you can't create and save your own, but on the Motif keyboard you can create or import your own arps via MIDI file. The factory ones though are AMAZING and more than enough, and go beyond basic MIDI loops, whereby they self adjust based on style and how many keys you're holding down.
In one final opinion if you have to get just one keyboard/module and you're set on having the integrated keyboard and some sampling/sequencing, get the Motif ES series. It may take you a little more time to adapt to the display, but spend some time with it in the store and you'll see it's quite intuitive. The Motif Rack ES version is a cryptic NASA control panel, but I picked it up over the full keyboard Motif because I was able to score it for $800 brand new.
If you've already got 'a lot of keys in your room' then I truly feel that the Fantom will be as someone said here 'another decoration' and you will be better off with one of the units I went with instead if as you mention - it all comes down to the sounds. Get something that will really be a step above and beyond something you already have.