Service Pack 1 was released for general download this week.
I've just let Service Pack 1 be installed on my laptop and wish I hadn't. It's turned my laptop from being pretty fast into something more like a bowl of treacle. It takes an age to start up and some programs are taking a long time to open.
I googled "Win 7 SP1 has slowed down my PC" and found a raft of other people complaining and the usual suggested course of tests / solutions from Microsoft, none of which work.
So be warned; I suggest taking a disk image of your PC before installing it.