Poloniex - is it wise to keep all your cryptos on a single exchange? No...

Right now 60+% of all Ripple being traded is on poloniex!

I get that poloniex is the the most well known, and for the most part works but in the recent weeks they claim to suffer from multiple ddos atacks. Whatever the reason for all the hangups, doesnt really matter a whole lot.
Either way i think keeping all your cryptos on one exchange is asking for trouble, and at some point people will suffer losses. Not a case of if but when... mtgox ring a bell?
I have nothing against poloniex and would say the same thing to anyone keeping all their trading on one exchange because it can and will happen on any of them.
Another thing worth mentioning - it appears in the past xrp price has suffered directly from panic selling on poloniex related to ddos attacks. It seems like every time xrp has a rally the ddos attack is there waiting to suppress it.
The rally on march 28-april 2nd saw xrp reach 7.4 cents usd, and within a few seconds of getting there dropped to 5 cents... many attributed it to the ddos attacks.
I think it would be a very wise decision to split up our accounts between 2 or 3 exchanges.

Anyone disagree?