I had an EX7, very similar to the ex5.
It sounded great, but yes was very buggy too. That was a while ago.
The instructions for the EX5/7 suck. any yamaha instructions suck, makking navigation rough and unpleasant. But see for yourself.
Always read the manual before you buy a synth. It helps oout alot.
the EX-5 has sampling capabilities, which is a huge bonus. I think the MOtif 7 does too but Im not sure, im not into all-in-one synths anymore. I keep my keyboard rig modular with midi controllers.(cause you can break the keys with out breaking the synth!)
All in all, i do not recomend the EX5, anything yamaha, (except A4000/5000) or anything built by roland in the last 10 years.(crappy ROM synth sounds)
Korg makes some good sounding synths, If i were to buy a new one, it would probably be a korg, but hey.... Thats me.