ive read some posts talking about the evga 90 day upgrade on there cards, i was just wondering what exactly is this?

You buy an evga card register it with them and upload your invoice.  You then have 90 days (from purchase date) to do what is called a "Step-up".  They credit you however much your card cost toward the card you want to step up to.  You pay the difference plus shipping both ways.  

^what he said. You should also note that the prices are based off of what EVGA is charging, not necessarily what you paid for the card.

The rub is that you have to pay whatever EVGA is selling the cards for on their site.  Those prices pretty much don't drop (or do so very slowly), much slower than the market price does in some instances.
 
For instance they're still asking $360 for their 8800GTS 512 even though you can find it for $200 to $250 most places.
http://www.evga.com/products/prodl [...] ies+Family
 
But San Pedro is right -- you mail them back your card, the difference in cost[1], and shipping, and then they send you back a card.
 
[1] EVGA Price on new card - What you paid retail

I paid $290 for the 8800GTS 320MB card last year.  When the 8800GT came out it was listed at $270.  I stepped up by paying the shipping both ways.

I hear BFG is starting a step-up program as well.  I also heard they give you the MSRP for your old card, if thats true it beats eVGA.