I had been having really bad issues with my 2010 iMac freezing up for a few seconds every couple of minutes since upgrading to Mavericks, and yesterday I finally decided to do something about it. I spent a good amount of time digging through Console.app and finding problem spots in the event logs, running tools like OnyX and CleanMyMac, and digging through various system files. Here's what I did to get it running like butter again:
* Reboot into recovery mode (hold cmd-R at boot) and run Repair Disk and Fix Permissions in Disk Utility (always a good idea just to catch any disk problems before you get going).
* Run EtreCheck (http://www.etresoft.com/etrecheck) and remove anything described as a problem kext or problem login item. For me the main culprits were Soundflower (used with Audio Hijack) and old versions of Paragon NTFS and extFS.
* Open up Font Book, click All Fonts, select all, and pick File > Validate Fonts. Change the dropdown to "Warnings or Errors", and when the scan finishes choose all the fonts with warnings or errors and remove them. This actually fixed a lot of weird issues with Chrome and other apps.
* Run OnyX (http://www.titanium.free.fr/downloadonyx.php) and run pretty much every verification, maintenance, and cleaning task. Don't forget to go through the sub-tabs in each section. Also, read the help if you don't know what you're doing. Delete ALL the font caches (in the Cleaning tab) and reboot.
* Run CleanMyMac (or similar tool) to get rid of old logs, unused garbage, etc. Get rid of any old applications you don't use anymore and all their garbage too. Extensions Manager in CleanMyMac will help you track down login items that you don't know you're running.
Basically, the problem for me ended up being that I had been migrating my profile, development tools, apps, and other stuff from Mac to Mac since 2005. It seems like everything was mostly ok until Mavericks, when Apple clearly made a lot of changes under the hood and all that really old garbage all over my Mac ended up freaking the computer out.
After running all of the above stuff I haven't had any of the aforementioned issues. I'm planning to upgrade this old iMac pretty soon, and I'll definitely be starting fresh and not using Migration Assistant. Luckily, everything important these days is synced up with Dropbox or Google Apps (something that wasn't so easy in 2010) so it should just be a matter of reinstalling all my applications.