As has been said, "TCAS" - especially in most GA aircraft is prone to drive a head down and inside - and the display doesn't always give a "class D" bearing on the target especially in a turn. Worse, in a climbing turn the relative vector can be reducing and in error laterally and vertically.
I fly an aeroplane so fitted and that in nil wing can give a ground speed of 3nm/min. The closure on something heading directly towards doing the same is minimal at best - I've seen pilots spend so long trying to identify where the threat is 'on the screen' before looking up and out. It's a mindset of 'automatics' will keep me safe and that is to the detriment of good old fashioned airmanship, situational awareness and TEM principles.
I'm a big fan of TCAS - in a well equipped aircraft with a well trained operator in seat 0A but there are so many other threats that aren't necessarily going to show on the screen - (hang gliders, parascenders etc). Not to mention in a supposedly safe environment (the circuit, perhaps) where the pilot doesn't understand the inhibit function or the capability of the systems that recognise the environment and desensitise themselves leading to too many 'contacts' in a target rich environment that the conflicts become so frequent that the pilot begins to ignore the warnings.
I stand by my statement that, whilst good, it isn't the solution