Window version wallet occupies a lot of memory and CPU percentage, making the computer extremely slow.
Here's what I'm seeing here while testing the Windows GUI version:
Re-indexing takes about about 10 minutes and consumes 1.38GB. If a system has less than that free memory available (after accounting for the OS and other programs), it's going to slow down dramatically as it begins paging, and this could become a very very long operation at that point.
I have sufficient memory on my system to avoid paging, so after re-indexing my cpu usage dropped to a normal 1-3% for the client. But memory stayed at 1.38GB for the duration of that session (my guess is another memory leak in the blockchain code). After restarting the client, my memory usage dropped down to the expected range (~571MB).