Sorry, looks like i accidentally erased my post on VIX ETFs - I am still learning how to use this interface and it is a little less than intuitively obvious. My apologies to my two colleagues who took the effort to read and comment.
The following wikipedia entry explains why it is not possible to replicate vix using s+p options:
'The VIX is calculated as the square root of the par variance swap rate for a 30 day term[clarify] initiated today. Note that the VIX is the volatility of a variance swap and not that of a volatility swap (volatility being the square root of variance, or standard deviation). A variance swap can be perfectly statically replicated through vanilla puts and calls whereas a volatility swap requires dynamic hedging.'
One would have to hold a square root of a position. Nevertheless, premium on vix futures does represent additional premium on top of s+p option premium - there is probably room for trading this fact even if it is not honest to goodness (risk free) arbitrage.