I also own one - and use it for gigging. No, it's not as light as the Casios but, even for a 55-year-old with a screwy back, it's doable. I use a Road Runner bag to carry it around - it adds very little to the weight but I keep a close eye on it for rips and stitching problems.
I don't use the stand that came with it - Gyro's right, it's not suitable for quick stage set-ups as it requires a screwdriver. I use a lightweight Z-stand plus a home-made device to stop the pedal wandering around.
Because it has such a good action and is very expressive, with excellent acoustic piano samples, I find it a joy to use for gigs in more intimate surroundings. The electric piano samples are not to everyone's taste - I prefer the more pure Rhodes and Wurlitzer samples that can be found on other digitals - but I have adapted to them. The fact that it has decent built-in speakers/amplification is useful for on-stage monitoring when we're playing these quieter, smaller gigs. It;'s also nice not to have to hook it up to an external system for solo practice and general in-home use. For solo gigs, I would expect that, beyond the smallest, quietest venues you'd probably want some form of external amplification. The new JBL, Yamaha, Peavey and Mackie 10" powered amps are great with pianos, despite their small size.
For rockier/louder gigs, I don't use the Korg. I have a Roland RD300SX as my main board, which has a lot of useful extras such as registration memory, a dedicated "dual" button and a wide range of effects. However, I'm not impressed with the action (hopefully better in the newer GX model) and it has no built-in speakers. The latter is not an issue for rock gigs as my keyboard stack requires that I use louder external monitors or in-ears.
I have compared the Casio PX-320 alongside the Korg SP-250 to see if I could get away with using the Casio for our smaller gigs. My conclusion was that the quality of sound, action and expression from the Korg exceeded the Casio by a fair margin. Of course, that is only in relation to my style of playing - YMMV!
One new board on the horizon is the Kawai ES6. It looks like it weighs about the same as the Korg and has built-in speakers. Demos of the main sounds can be heard here: http://www.kawai.de/es6_en.htm
Anyway, good luck with your search.