I've checked the kindle forum on amazon, tried rebooting and limiting number of books downloaded to under 400 but my kindle still takes a long time to move around within the device.  Once I'm reading a book the pages turn ok but anything else is very slow.  I ran into a woman who has gone through two kindles that had battery failure (while under warranty) but battery isn't my problem.  Anyone else having a problem similar to mine?  If I can't resolve the problem I think I'll try Nook instead.

I have noticed my Kindle working slowly the last few months. The first thing i was going to say was to decrease the amount of books on it. Thats what I was told by the lovely ladies of this forum. However I have not yet sorted through mine to remove some. I really need to do that soon. If thats not the problem though, then I dont know what it could be.  Its the same as yours though, once the book is opened and your reading then it works wonderfully, but anything else is slow.....searching through collections and such.

Have you updated to the newest software?    Your not saying which Kindle you have but I have K3 keyboard WiFi & 1500+ ebooks & 20 games   still going fast! 

I have the Kindle Keyboard and mine was a little bit slow before this recent firmware update.  I installed the update and put a parental lock on the archives, and it's working great now with 700 items on it.  I'm not sure if it was the firmware update or locking the archives, but it's working just fine.  I have a huge archive (~3000) and I've heard unsubstantiated rumors that this can cause some slowness.

A couple years ago, I had a case where it was so slow I could barely move from one book to another.  Resetting did no good.  I called their tech support, and they walked me through deleting some index files, I let it sit plugged in for 24 hours to re-index itself and it was fine thereafter.

Try giving Kindle support (not the general Amazon number) a call.  They're usually extremely helpful and knowledgeable.  Don't bother emailing them.  If it's anything more complex than a reset (which you've already done), they'll just reply with an email telling you to call them.  If nothing else, they can make sure you have the latest firmware.

How do I know I'm calling Kindle support instead of general Amazon support? I frequently have issues with my Kindle Fire and have to call what I thought was Kindle support (or, rather, have them call me).