Hello I've just upgraded from LR 2.7 to LR 3.6 in the last month or so.
I am running Windows 7 64bit professional and have Photoshop CS4 on my machine.
Before the upgrade rendering 1:1 previews wasn't exactly fast but it wasn't too bad. I've just been rendering 1:1 previews for just 550 images and it has taken over 45 minutes to do so.
That seems "normal" now. LR 3.6 seems to be slower at working. (And yet I hear that LR 4 is even slower. Thankfully I am not in a hurry to upgrade to that.)
I heard that using the second screen with Shift+E or Shift+G etc can slow down rendering so before I render I now close that second view. I have not noticed that this makes any difference: rendering still seems to take forever.
The machine isn't exactly under-specified. Intel Core2 Duo E83400 @ 3.00GHz, 8GB of memory and disk space aplenty.
That's a relatively old cpu. And you're around 5 seconds per image, which isn't all that bad. You don't say how big (in megapixels) your images are.
You can start rating and keywording images as soon as the first one is available, and at 5 seconds each, LR will stay ahead of you and finish well before you do. That 45 minutes shouldn't make a real difference to you.
It is funny what we each think of as "relatively old". Three years since I purchased the PC. It works fine for everything else that I use it for but the change between LR 2 and LR 3 has been quite marked in terms of rendering speed. I would say it is far more than a doubling. If it were only a "little bit" longer I wouldn't mind but this is distinctly annoying. The images are off a 5D MKII so 21MP.
As for keywording as the first one is available that makes an assumption that this issue is at import. Indeed I keyword in bulk at import via metadata preset and typing in keywords so I don't have to touch the images at all until they are ready to review.
Yes import rendering is slow but in this case I am working in develop mode. I had just gone through and done batch white balance adjustments. At that point my practice is to re-render the images before I do fine w/b adjustments and adjustments to exposure and black point, this means that there is less delay between opening an image and it "loading" ready to work on. However the huge delay that it causes is making me re-think this and possibly suffering the "loading" delay instead.
Most of the changes for LR2 to LR3 have been good (the notable exception being slideshow which is no longer useable). This however is not a good change.