MBP slow/ beachballs

I have a 2011 15" MBP. I upgraded the RAM to 8GB and have a 750GB HDD. Over the past few months I have noticed that the machine has slowed in its performance. I get beach balls constantly, even when closing programs. iPhoto takes a long time to load and beach balls when I open and close out. Also Safari will freeze on websites and/ or take a long time to load. I have not downloaded anything suspicious that I know of, but my wife uses my computer and there is no telling what she may have done but I doubt she downloaded anything.

My question...is there something I can do to maximize performance? Is there a way to check for rogue software? I have read several posts saying there is no need, and some that recommend scanner software for Mac.

Any suggestions?

Please read the "Beachballs" link in my signature. With 8gig of ram…amount of ram shouldn't be the issue…it does help to reboot the computer every so often.

Other that this (and what's in the link)…there is always the possibly that the hard drive is going bad…but usually unlikely on a newer computer.

- Nick