I think that the main reason for the launch of the new gTLDs is simply that the traditional TLDs, COM/NET/ORG and the recent gTLDs and sTLDs (BIZ/INFO/MOBI/ASIA/NAME/TEL) etc were being overtaken by the ccTLDs and growth was shifting away from these TLDs towards the ccTLDs. Only .COM was really keeping pace but that's due to it being considered a 'must-register' option for new businesses and users registering their .ccTLD domain.
While some new gTLDs definitely target a clear and as yet unserviced market, others are simply landgrab attempts. It bothers me that some of the people pushing the new gTLDs were also heavily involved in Domain Tasting. A lot of the public now realises that the Landrush phases for many of these new gTLDs will be rigged with the high value single word generics being reserved by the registries for sale at inflated prices.
While the concerns about confusion over extensions and network security are valid, the real issue is that faced with an overwhelming choice of new gTLDs, the public might opt for the TLDs that they know - the ccTLD/COM axis (it typically accounts for over 80% of the domain footprint in most countries) will probably get stronger.
In terms of name collisions, I see them quite regularly when running the monthly statistics updates for DNSes. Some businesses or users decide to invent their own ccTLD or TLD and it is then added as a reverse DNS entry for the nameservers in the publically acessible DNS for their domain name. The other aspect, something I saw when I ran a full gTLD website > IP mapping survey earlier this month is the proliferation of private IP range (10.bbb.ccc.ddd, 192.168.ccc.ddd etc) IP addresses being used as the IP for websites.