This started a few months ago with LR 5.7 and is still happening with my upgrade to LR 6. The question is not about a slow import but the import dialog window freezing up as I select different Import options.
My usual workflow is to just copy the images from my CF card to a folder on the desktop where I do a basic cull and discard anything I won't want to use. I then choose the Import option from the File menu and the Import window appears as one would expect. I click on the Source folder and the images instantly appear in the center section with check marks as they should. Everything is normal so far.
I usually have the Copy/Move option set to Copy as a DNG but if for any reason I want to choose a different option like Move or Add the program at this point usually freezes up or stalls out. I'm on the Windows 7 platform and I just get a little spinning wheel where the cursor was which usually means the computer or program is searching for something or thinking (yes I know that's not the right word).
After what seems like a minute or 2 the screen flashes for a split second and then I can go on to the next step, like editing my File Renaming choices but then it almost always stalls out again and sometimes it can be for 2-5 minutes. Once again it flashes for a split second and then I can move on, I then have to choose the Destination and hope it doesn't freeze up again before clicking on Import. I don't even mess with Keywording or anything else as it would only add to the time to get to Import. If I get impatient while the LR is snagged in this holding cycle and click again on whatever choice I was making I get a "Lightroom is not responding" up at the top of the program window. Once I am able to click on Import it works fine and the time seems about right depending on the amount or size of the images I am processing.
It's gotten so annoying that I sometimes just catch up on news or email on the second monitor while LR spins the little cursor wheel.
As mentioned I am running Windows 7 and have a pretty high end machine with an I7 processor, plenty of room on the main drive and 16GB of Ram. Not sure what else is relevant. I run LR on my laptop when out on the road but have never had this happen there, only on my desk top computer and it started about 6 months ago.
If I was importing from a card reader I might suspect the logjam was there or maybe a bad USB cable or socket but I'm working with images on my C Drive desktop. Doesn't seem to matter if it's a big batch of images or a small one.