How long until the LGA 1155 becomes obsolete?

Ivy Bridge is most likely the last CPU generation on LGA1155, Haswell will have LGA1150.

1155 is being replaced April/May next year.

That's a good point, but the OP did ask about the socket and not the CPUs. Maybe he worded it wrong though, so good clarification  

I personally would not worry about how how future-proof any given socket might be since my systems are usually not worth upgrading by the time I feel like I need to upgrade.

The only PC I owned on which I bothered upgrading the CPU was a P90 which I upgraded to P233MMX. My PCs after that had good enough CPUs to last until the whole platform was hopelessly outdated.

agree with the "still being useful" part above. I still find my 775 useful... ( and almost in need of an upgrade ). However, in the greater scheme of things, before you or I can purchase these they are already obsolete. Newer versions are already in the works as are their replacements... ( new design, new socket ).............

Best answer selected by roxas2030.