Besides security issues and not having the most up-to-date features, what would be the biggest concern? Could the software break from a host upgrading php/mysql? Could new browser versions cause serious bugs?
I see many forums running old old versions. I assume they must tweak things to have everything work correctly with the latest Firefox, IE, etc...
Just something I was wondering about with vb 3.8 coming to an end.
I suppose the best people to ask would be Kier/Mike in relation to vB, but running EOL software just means you won't have as much support, you'll be prodded at to upgrade constantly, you won't have access to bugfixes and the latest code implementations. There's not much else... apart from browser compatibility but you'd have to have some pretty old software for it to cause any major browser issues.
Zero support (generally, most software houses will tell you to upgrade to the latest version). No bug fixes (again, told to upgrade). And no security fixes.
There is also a possibility of incompatibilities with newer versions of PHP and MySQL when your host upgrades. Browser incompatibility is possible, but unlikely. (IE8 aside, it broke a hell of a lot when it was released)
This is all from personal experience, mind you, so your mileage may vary.