I have a motif, 4000 and use softsynths. No disrespect to the motif, its been a good workhorse for a while now. Its got a good solid fundamental sound set. However, I've been investing heavily in hi-quality akai format cd-roms that I load into the 4000. While the motif sounds are good(sometimes in this game, good aint good enough), the cd-roms are amazing and have a seemingly unlimited pallet of sounds available. (tip: max out your 4k memory)
I have about 25 cd-roms that I have saved to the 4K hard drive so my library is allways conveniently available. If I have to go work at another studio, I just grab the mp and my entire library is with me. Or if the studio already has a 4K, I can just <dump entire memory to cd> and whatever song and all of its sounds are loaded to a cd-rom.
I use the mp to sequence my softsynths (Albino sees much action). I use a host program called bidule
http://www.plogue.com/index.php?option= ... &Itemid=35
I then sample my vst parts into the mp using the optical in.
I haven't really used the 4k to generate synth sounds too often, but I just ordered a disk with all Access Virus samples to try. I love the sound of the Virus and will buy one if the cd-rom doesn't get close enough to the real deal.
As for the motif, I pretty much use it for rhodes, wurly and piano sounds now, and a as a controller.
If you're a hip-hop or rnb pruducer, don't even think about using stock motif drum sounds in your music as they are for the most part, crap.
Use what works for you.