Nothing wrong with OnyX, it is only a good interface for existing OS functions. Of course it will slow things down until the various caches re-populate. It has sorted problems for me, especially wifi connections and bad cookies.
I think some people are having Spotlight re-indexing which slows things for an hour or so. If you click on the icon in the top right corner of the screen it will show a progress bar, but don't watch it unless you like watching paint dry.
The CUI problem is being blamed on the 10.7.3 System Update, but then I know very many people who have had no such problem at all. There is good advice here as to what to do.
If you are wise you will already have an external bootable backup clone. The full installer is available on MAS and it's a good idea to download it eventually (after the servers are less busy) and copy it to the clone.
@MetaJustice - I agree. I just installed the Lion OS update 10.7.3, using the combo update recommended by you and several others; no problems thus far. All iLife and my main programs (Aperture, Photoshop, Pages, etc.) all seem ok.
I did reset Home folder permissions and ACLs and felt good that it confirmed my USB Flash Drive Restore Lion worked.
THE BEST NEWS: HTG: My Internet download speeds DOUBLED!
Doubled - Because, next week, I'm getting a new modum, first wifi router and new faster Internet connection, I got into testing my actual Internet speeds now so I could do a 'before and after' -- testing them on three sites.
Since I had bookmarked the sites, had the 'before' data, I did it after the new Lion OS install (and resetting Home folder permissions for the first time in a long time): Double the speeds; quite incredible.
Now if the new modem, new faster Internet connection lives up to promised claims, I'd be a very happy camper...i.e. computer user.
MegaJustice This is the best advice for Mac maintence that I have ever recieved! working today proved to be stress free and like it should be, I somehow forgot what it was like, but now I feel reunited with the Mac that I once took out of the box - sounds a bit like a love story - it is! I'll have to share this with friends!