MacBook Pro (Mid 2010) suddenly become very slow

Hello community!

My MacBook Pro (Mid 2010) has suddenly become very slow at boot time: I see the grey Apple logo and the "spinning lines" for up to 5 minutes (haven't timed it yet, but feels like).

After the login screen finally appears it still feels very sluggish: when I click on my user for instance it takes another 10 seconds until the password field is shown, and sometimes the spinning beach ball quickly shows!

When I finally have managed to login application startup is ridiculously slow, e.g. sometimes over a minute - again not timed accurately, but for sure 5 times as long as it usually would take. Starting up preferences takes a long time, everything is slow at startup and the beach ball keeps appearing.

Basically I observe all the symptoms described here:

http://appletoolbox.com/2010/05/continued-macbook-pro-mid-2010-beach-ballsfreeze s-apple-replacing-testing-units/

CPU usage is almost zero during these waits, but the beach ball keeps appearing for several seconds sometimes. The Apple DiskTool reports no errors either (I know, doesn't detect all failures), the system info sais the initial startup test was "successful". I did not find any free utility to check RAM yet, will boot with a Linux DVD later on and try to do some more hardware checks...

I have no external drives attached, no USB sticks inserted, just a plain "out-of-the-box" MacBook Pro 11", with the standard 250 GB Hitachi disk drive (the link mentions that initially mostly Seagate drives would be the culprit, but other harddisks seem to be affected, too).

Now here's the thing: when I say "suddenly became slow" I mean that Lion (currently 10.7.1, but am updating in this very moment) ran JUST FINE before! However I noticed it the first time when I connected a HDMI TV display during boot, the display simply wouldn't be detected, so I rebooted, and since then, slow bootup and application startup times.

Now I am not 100% sure whether these slow startup times actually appeared after the update to 10.7.1, as I do not use my MacBook Pro very often (the one I use for work, my iMac, is still on Snow Leopard for productity). But I think it also did run fine under 10.7.1 at some time.

And no, I don't remember installing any special software which would explain this change. Disk is not (yet) encrypted with FileVault. or any other software (and never was).

Once an application is running I detect no slowdowns, e.g. graphic performance seems okay and I have no random crashes which would indicate bad RAM. It really seems related to the harddisk.

And now while writing this I have the feeling that after 15 minutes or so of work application startup seems to normalise, that means now when I start other applications (which off course I did not start yet during my session 😉) they seems to startup in a reasonable time.

Any ideas? The above link (and other similar issues I read here in the forum) seems to provide no real solution (except that buying a new harddisk seems to help - but who knows, the problem might just creep in again). Just now I'll reboot and install 10.7.2 and see whether that makes any difference... holding my breath...

Thanks all for any ideas!