It depends on how you look at it. The best solution should be a weighted average of few exchanges.
The 'best' solution depends on why you are seeking a rate in the first place.
I think the point of showing their rate based on a single bid price is that it is simply passing on the rate it will be getting itself for the conversion.
This is exactly the point.
For example, if you intend to buy/sell bitcoins on BTC-E after your trade with someone from localbitcoins.com or after purchasing something with bitcoins, then the rate on BTC-E is the only one that matters.
Nothing wrong with using the Mt Gox rate if that's where you dump coins or replenish your stash.