This issue persists despite the various upgrades. I have a top spec machine with an SSD hardrive and a 100Mb internet connection (London based). Mist has behaved like this from day one and it did the same thing on a slightly older machine too. I'm running the latest v0.9.3.2075.

Yes, wiping the block data and starting afresh resolves it (I get a fast sync) but give it 2 weeks and it's on a slow-go again. Updating 2 weeks of chain data can take an entire day on a 100Mb connection. I'm sure it would behave the same way with even a 10Mb connection and the problem is the way it's handling the data.

Check out the video which shows the snail-pace sync:

https://youtu.be/HqEyog_Ueo8