LightRoom3 LR3 - Spot Removal tool soooo sloooooow

Question

LR3 is generally working fine for me.
It was slow to start with, but I saw that it was doing a lot of disk acivity in the background when I upgraded from 2.7 -> 3
I left it alone to do it's think and it's been fine for the last week.
BUT .... one thing thats changed (for the worse) is the spot removal tool.
It's so slow it's beyond a joke.
It almost looks like it's trying to completely render the image where I'm only interested in a small part of it changing.
Where I could adjust to the pixel and release it to re-render, now I get to move the spot destination swab for about 4 seconds then it stops .... and I have to wat for almost a minute for it to finigh picking it's nose (or whatever it's doing) before it comes back.
Then I have to try fine tune it again, but if I don't get it right then I either have to guess it or wait another minute before it lets me move it again.
I have an i7 CPU and virtual CPU #4 goes 100% while it hangs. All the rest bounce about at 10-15%
So frustraiting. What should be a quick atch/repair tool has become unusable.
My only workaround is to export to CS and patch/clone in there ... unless it's sensor dust in which case it can take up to 20 minutes just to de-spot a picture and batch process across a set.
PC spec:
XP64 SP2
i7 CPU
12Gb DDR3 1866
SSD primary and scratch disk (same one partitioned)

Answer 1

Right .... I think I might have cracked it.
I noticed that TIF files were much worse than .NEF or .DNG.
The Raw files would be a bit more tolerant and I tried setting the write to .xmp to [on] and it improved a bit, but after a bit of editing it would become sluggish again on all tasks ...
If I switched off the [xmp] write AND the "Include metadata changes in TIFF/JPG PSD files" it becomes a lot more responsive.
All I have to do is Ctrl+S after I'm done and the Metadata is written (within a second).
I think that LR keeps trying to constantly update the metadata and catalogue + render all together and it couldn't keep up (even though I use SSD and have an i7 with 12Gb 1886 memory).
I also had an extra boost by telling the system to create 1:1 previews of the files I'll be editing. This takes some time depending on the source data  sizes and compression (go make some tea), but it improves performance by doing all the initial start-point rendering in advance rather than on the fly.
I can now work at normalish speed again (Yay!). It is still a bit more clunky than LR2.7, but it's useable again and it is faster in other areas.
NOTE: By switching off the auto-update XMP and Metadata features, you could potentially lose edit updates to your files and updates don't transfer when the files are opened in other apps.
To avoid this you only have to do the Manual save of changes to the files by pressing Ctrl+S or manually in the menu:
Metadata | Save Metadata to File
After you do that all other apps pick up the updates to the files