I am building a new system and I want it to last a long time. I am wondering whether I should get a mobo that supports SLi or not.
In the future, to keep up with technology I'm going to upgrade sometime. I don't know whether I should get an SLi mobo now so I can just add another GTX 460 in the future, or if I don't get an SLi MB I would sell my GTX 460 on ebay and buy an up to date card.
What would be the most cost-effective solution for upgrades in the future?
Later on you might want to add a card for PhysX or to help with GPU accelerated software or just to give it a boost for future games so I'd also say yes: The cost is minimal and adds flexibility to the build.
Yeah, but my mobo only supports XFire not SLi. If I really wanted I could send back my power supply and get a 850W or something, and as it happens the graphics card is broken -- so I could ask for them to send me back an AMD graphics card instead.
I'd swap for an AMD card, if possible upgrading it when you do, just make sure the existing PSU can handle it.
Later on you could go CF and add a stronger powersupply to cope but cards get more efficient with each new generation so it may be better to just swap for another card when the time comes rather than take the CF upgrade route.
Only the future knows.