openSUSE feels slower than it should be, what to check?

I know it’s a common tendency for people to feel their operating system is too slow. In my case though, I’m getting the feeling that my openSUSE installation is running a bit slower than it was and than it should be. This mostly comes from the fact that it sometimes takes +10 seconds to open a fresh instance of Dolphin or Konsole or KWrite, which are considerably small programs so this is quite inexplicable! The RAM is almost never more than 40% full, nor do I typically have more than about 8% CPU used idly. I have an i7 920 processor and 9 GB of RAM, so this can’t be blamed on an old machine either.

Although it’s unconfirmed, I’m getting the impression that slow drive I/O might be at fault… if not then some kind of driver or Kernel setting. The OS is installed on a SATA2 drive, with my data on a SATA3… other than that I disabled all costly processes I was aware of, such as the evil Baloo file indexer. A problem I can notice and test directly is that if a process is using a hard drive, every other process that attempts to access that drive freezes for several seconds (goes into “disk sleep” mode) which is definitely a huge annoyance but I figure unavoidable. Anything else I can check?

Maybe smartctl would give a clue