No one else seems to be trading Linden to BTC so not sure what a better rate is. Obviously going through Linden for a USD buyer would be expensive, but for people who have Lindens (i.e. deal in SL) it's pretty cheap compared to the normal process to get BTC out of it:
Take 9010 Lindens and cash them out...
Wait 4-5 days for Linden Labs to process payout, pay $1 + a fee = $33.53
Buy liberty reserve with paypal (pay $0.30 + 3%) = $32.56
Buy mtgox with liberty reserve (pay 1%) = $32.23
At this point your mtgox account has $32.23 in it after 5+ days, at which point your Bitcoin might be worth $40 or more (and you still have to pay a fee to buy it). I doubt USD buyers will see SL as the way in, anyway, because Linden Labs has that absurd rule that prevents you buying more than $30 worth on a new account.
This service is primarily to allow Second Life players to cash out in Bitcoins effort-free.