I'd like to offer a slightly different perspective as I dont know your current situation. Whether you should do all cash really comes down to what that money means to you. Without making this overly long winded, if that money is anything but completely unnecessary for your day to day life, i'd think hard about it.
In other words, if you dont need that money in the forseeable future, then as everybody has said, cash is king and it WILL afford you discounts you wouldnt have other wise received.
However, if you are running deal to deal, or somewhat early on, OPM is the best by far. In that case you keep your cash in case you need it, and use everyone elses. Sure, it costs you 'interest,' but that is easily something you can just decide is the cost of doing business. Also keep in mind, there IS a cost to using cash. Its just most dont necessarily like to look at it from that perspective. :D
In the end though, there's no doubt, if you got it--CASH IS KING.