Safari causing full-system hang

Question

For a while now I've been getting the SBOD irregularly in Safari, since 3.x if I remember right. I've got some time off work at the minute so I'm finally looking into this properly, and here's what I've found:
There seems to be two separate conditions. The first happens on loading some, but not all web pages, causes a lengthy hang in which the entire system (even invoking Dashboard or Spaces) becomes unresponsive. In the console this accompanied by an entry similar to the following:
05/10/2010 08:15:47 /Applications/Safari.app/Contents/MacOS/Safari[242] ATS AutoActivation: Query timed out. (elapsed 5.0 seconds. params: queryString = {comapple_ats_namepostscript == "Helvetica-Neue" && kMDItemContentTypeTree != com.adobe.postscript-lwfn-font}, valueListAttrs = {<CFArray 0x6f5710 [0xa008dee0]>{type = immutable, count = 1, values = (
0 : <CFString 0xa01602c8 [0xa008dee0]>{contents = "kMDItemContentType"}
)}}, sortingAttrs = {<CFArray 0x6f5730 [0xa008dee0]>{type = immutable, count = 1, values = (
0 : <CFString 0xa01603a8 [0xa008dee0]>{contents = "kMDItemContentModificationDate"}
)}}, scopeList = {<CFArray 0x6f5750 [0xa008dee0]>{type = immutable, count = 1, values = (
0 : <CFString 0xa0161a98 [0xa008dee0]>{contents = "kMDQueryScopeComputer"}
(sometimes it names a font, sometimes the font name is "_")
I suspect this means some vestigial adobe product has messed my system right up. I used to use CS4 but have long since removed it. I also have Air and Flash (the current gala beta) installed. I have had fontbook validate Helvetica Neue and check all fonts for duplicates - if external disks are plugged in at this time they all spin up.
The other case is when downloading a file through clicking a link or alt-clicking a link (right-clicking a picture and saving it to the downloads folder does not cause this behaviour), and is accompanied by this much sparser line in the console:
05/10/2010 08:25:06 kernel disk0s2: I/O error.
The files themselves can be opened, moved and copied without incident and at regular speeds, so I doubt disk corruption. I've also performed a few full clone/restores on my boot disk with no effect. My initial thoughts were to blame a long-forgotten folder action that sorted downloads into different places (including a network share, if present), but disabling folder actions has not helped.
So, any ideas? I'm fresh out.

Answer 1

A workaround for the font-problem seems to be to turn off ATS - it's in FontBook.
The second issue still eludes me.
Things I have tried:
Trashing ~/Library/Safari/
Trashing ~/Library/Preferences/com.apple.Safari*
Cleaning out every vestigial trace of anything suspect I had on my system (google keystone, logitech control centre, SIMBL, The Spark, iStat Menus, folder actions)
Interestingly, the issue is not present for the guest user, so it IS something wrong with my user account. I just can't figure out what.
Yes, making a brand new account would fix all this, providing I'm meticulous about testing the issue as I move /Users/Old/ into /Users/New/, but I'm kind of loathe to give up. It's surely something really simple!