This sounds really interesting, so I compiled a new build (with clang, yay :). Lace flicker is still there, as Gandalf points out. I was curious about the buffer setting, so I cranked it up to 50, which gave me this:
Process: x64 [31144]
Path: /Users/pelle/src/vice/build/cocoa-10.6-clang/x86_64/vice-macosx-cocoa-x86_64-10.6-clang-2.1.17/x64.app/Contents/MacOS/x64
Identifier: org.viceteam.x64
Version: ??? (2.1.17)
Code Type: X86-64 (Native)
Parent Process: launchd [155]
Date/Time: 2009-10-18 17:58:28.336 +0200
OS Version: Mac OS X 10.6.1 (10B504)
Report Version: 6
Interval Since Last Report: 17926 sec
Crashes Since Last Report: 1
Per-App Interval Since Last Report: 98 sec
Per-App Crashes Since Last Report: 1
Anonymous UUID: 5610CC0F-0D30-4256-9E8A-20B877605F9A
Exception Type: EXC_CRASH (SIGABRT)
Exception Codes: 0x0000000000000000, 0x0000000000000000
Crashed Thread: 0 Dispatch queue: com.apple.main-thread
Application Specific Information:
*** error for object 0x4088000000000000: pointer being reallocated was not allocated
Thread 0 Crashed: Dispatch queue: com.apple.main-thread
0 libSystem.B.dylib 0x00007fff86ba1ff6 __kill + 10
1 libSystem.B.dylib 0x00007fff86c43072 abort + 83
2 libSystem.B.dylib 0x00007fff86c31d25 szone_error + 519
3 libSystem.B.dylib 0x00007fff86b5bb1e szone_realloc + 102
4 libSystem.B.dylib 0x00007fff86b5ba7b malloc_zone_realloc + 92
5 libSystem.B.dylib 0x00007fff86b67b13 realloc + 169
6 org.viceteam.x64 0x000000010000f7c9 0x100000000 + 63433
7 org.viceteam.x64 0x00000001000ec9b5 0x100000000 + 969141
8 org.viceteam.x64 0x00000001000ea991 0x100000000 + 960913
9 org.viceteam.x64 0x00000001000d7b71 0x100000000 + 883569
10 com.apple.CoreFoundation 0x00007fff8166d35c __invoking___ + 140
11 com.apple.CoreFoundation 0x00007fff8166d22d -[NSInvocation invoke] + 141
12 com.apple.CoreFoundation 0x00007fff81688f21 -[NSInvocation invokeWithTarget:] + 49
13 com.apple.CoreFoundation 0x00007fff8166a37c ___forwarding___ + 860
14 com.apple.CoreFoundation 0x00007fff81666458 _CF_forwarding_prep_0 + 232
15 com.apple.CoreFoundation 0x00007fff8166d35c __invoking___ + 140
16 com.apple.CoreFoundation 0x00007fff8166d22d -[NSInvocation invoke] + 141
17 com.apple.Foundation 0x00007fff82d70498 -[NSConnection dispatchInvocation:] + 181
18 com.apple.Foundation 0x00007fff82d6e725 -[NSConnection handleRequest:sequence:] + 1138
19 com.apple.Foundation 0x00007fff82d6e020 -[NSConnection handlePortCoder:] + 765
20 com.apple.Foundation 0x00007fff82d6dcdb -[NSConcretePortCoder dispatch] + 49
21 com.apple.Foundation 0x00007fff82d371a2 __NSFireMachPort + 270
22 com.apple.CoreFoundation 0x00007fff8165c1fe __CFMachPortPerform + 366
23 com.apple.CoreFoundation 0x00007fff8165bf84 __CFRunLoopDoSource1 + 356
24 com.apple.CoreFoundation 0x00007fff8163464d __CFRunLoopRun + 4413
25 com.apple.CoreFoundation 0x00007fff8163303f CFRunLoopRunSpecific + 575
26 com.apple.Foundation 0x00007fff82d53958 -[NSConnection sendInvocation:internal:] + 1969
27 com.apple.CoreFoundation 0x00007fff8166a37c ___forwarding___ + 860
28 com.apple.CoreFoundation 0x00007fff81666458 _CF_forwarding_prep_0 + 232
29 org.viceteam.x64 0x00000001000c96d4 0x100000000 + 825044
30 org.viceteam.x64 0x00000001000cbf9c 0x100000000 + 835484
31 org.viceteam.x64 0x00000001000cc702 0x100000000 + 837378
32 org.viceteam.x64 0x00000001000ca882 0x100000000 + 829570
33 com.apple.AppKit 0x00007fff84c98c31 -[NSOutlineView _dataSourceSetValue:forColumn:row:] + 97
34 com.apple.AppKit 0x00007fff84d55bb2 -[NSTableView textDidEndEditing:] + 541
35 com.apple.Foundation 0x00007fff82cf9926 _nsnote_callback + 167
36 com.apple.CoreFoundation 0x00007fff8163fe4a __CFXNotificationPost + 954
37 com.apple.CoreFoundation 0x00007fff8162c7f8 _CFXNotificationPostNotification + 200
38 com.apple.Foundation 0x00007fff82cf0890 -[NSNotificationCenter postNotificationName:object:userInfo:] + 101
39 com.apple.AppKit 0x00007fff849e6541 -[NSTextView(NSPrivate) _giveUpFirstResponder:] + 571
40 com.apple.AppKit 0x00007fff84a2b9a8 -[NSTextView(NSKeyBindingCommands) insertNewline:] + 485
41 com.apple.AppKit 0x00007fff849e5e09 -[NSTextView doCommandBySelector:] + 293
42 com.apple.AppKit 0x00007fff849da78b -[NSKeyBindingManager(NSKeyBindingManager_MultiClients) interpretEventAsCommand:forClient:] + 1966
43 com.apple.AppKit 0x00007fff849d9c9c -[NSTextInputContext handleEvent:] + 737
44 com.apple.AppKit 0x00007fff849d994e -[NSView interpretKeyEvents:] + 186
45 com.apple.AppKit 0x00007fff849d9727 -[NSTextView keyDown:] + 819
46 com.apple.AppKit 0x00007fff8494b6a9 -[NSWindow sendEvent:] + 8803
47 com.apple.AppKit 0x00007fff84880122 -[NSApplication sendEvent:] + 4717
48 com.apple.AppKit 0x00007fff84816acc -[NSApplication run] + 474
49 org.viceteam.x64 0x00000001000d54a1 0x100000000 + 873633
50 org.viceteam.x64 0x00000001000d368e 0x100000000 + 865934
51 org.viceteam.x64 0x00000001000016d4 0x100000000 + 5844
Scrollers appear more stable though, really nice!