Sold the BK5 so now I'm considering an alternate setup to keep around. The Privia PX350 keeps piquing my interest. But I do have some questions.

1. How are the built-in rhythms? I only use a few now on my s950 - big band, country 2-step, 6/8 Rock Soul, and a couple more. What do the Privia rhythms sound like? What about variations, starts and stops?
2. What about MIDI/mp3 playback? I rely heavily on midi and am getting into mp3. What kind of system do they use? Is it pretty straightforward or is it too simple or difficult to use?
3. What about onboard controls? What works well and what doesn't?

At $800 or less, just the piano stuff is interesting, but could I use it on a gig and not make a fool of myself trying to use the rhythm section and the USB MIDI playback off the sequencer. I'm looking for some YouTube demos, but they're hard to come by. If anyone has any knowledge or experience with the 350 or the previous 330 series, please help.

I have one and got it as a replacement for my real piano I had to sell. As a Piano the feel and sound are superb. Definatly use an out board sound system. Built in speakers are OK but don't do the sounds justice.
The rhythms are probably not on par with what you are used to. But for a laid back cocktail hour, dinner music, or just jamming they'd be just fine. They have a few basic intros, endings and 1 variation for each. You can edit them to some degree, changing instruments, volume , etc.
As far as MIDI it has it and thats about all I can tell you -LOL. I midied my BK7m to it and no problems.
It does support a Thumbdrive so you I believe you can do MP3's on it. I haven't really done much with it except just straightforward play it with a few keyboard sounds and some Rhythms. You can download the users manuel online.
All of that other stuff and most of my time is spent on the BK9.
My opnion is its the best buy for a solid home keyboard or for simple gigs. And very good to keep your piano chops up.
Lots of band players are using its brother the PX5s (4 programmable splits as a midi controller, lots more editing of sounds, no rhythms or speakers ) along with a second keyboard like the Roland VR09 to cover all the bases.

It's really a shame the Yamaha DGX650 is not a bit lighter and little narrower to carry around. It has everything you would want. A great action, great CFIII concert grand piano voice. 128 note polyphony. Styles quality from higher up arranger keyboards. Great additional sounds such as guitars, strings, brass, etc. Audio input for plugging in a mixer with mic or using just plugging directly in a iPhone, etc. to play songs. A USB input for playing and recording .wav songs or recording anything you play or sing into the keyboard. Internal speakers which can be shut off or kept on while going into an external sound system. I just wish it wasn't around 35 lbs and just a little bit thinner. It would be the perfect $799 gigging keyboard.
I sell the Privia PX350 and my few gripes would have to be that the styles themselves are ok but the drum kit sounds are just not up to Yamaha or Korg quality still and I wish the strings were better. Everything else as stated is a real plus for something small and light enough to carry around to jobs.

George, what about the Yamaha Piaggero?

It's not 88 weighted keys. It only has 76 semi weighted which is just like the YPG235 keyboard. The piano sounds, styles, etc. are just not nearly as good as the DGX650.

My main beef with all of the Casios is that they lack any kind of sync stop, arranger hold setting, memory, or "stop accompaniment" function for playing rubato with chords and auto bass.

Feature-wise the much better option is an 88-key piano controller MIDI'd to an arranger module, or mounted organ-style just below the keybed of a current MOTL arranger.

I admit i've been looking at Clavinovas and even the Kohler KD-60 (which is a Korg Pa80 in a furniture cabinet.) These are fully-featured arranger pianos. But they aren't even close to being portable!

For the price, Casio's keyboards have a fantastic feel, a decent piano sound, and they're light with a great price point.

I own the PX-350. I would not use it live as an arranger. Why? There aren't many styles, the styles only have two variations, the styles are good, but not great, the buttons aren't lit up, there aren't many buttons to control the styles, like auto fill or the stuff Ted mentioned.

I would recommend using it with a laptop and performing along with MIDIs. I use mine at home with Ivory II, and I'm in piano nirvana.