1) the next release of calibre contains changes that let us speed up metadata syncing during connection. On my Galaxy Nexus with 1000 books on it, the time went from around 4 minutes to 20 seconds. I can't guarantee everyone will get this increase, but it will be faster.
2) We are improving CC performance at startup and when grouping. The next release of CC (1.7) has the improvements when not grouping; application startup on my galaxy nexus with 1000 books is now close to instantaneous. Tomorrow's job is to do the same thing to grouping.
3) The next CC release (again, 1.7) improves performance when flinging by delaying drawing the cover thumbnails. It can look a little odd seeing coverless books flying by, but the benefit is that they actually fly by (on my phone).
4) Some people have posted 1-star reviews on Google Play saying that they are having licensing problems. We believe we have fixed these problems in CC release 1.7 by working around problems caused by using multiple google accounts with Android 2.3 devices. We can't leave comments on Google Play so I mention it here in hopes they will notice.
A plea: we are making very fundamental changes in CC, which increases the risk that we will break something. Please do not hesitate to post on Mobileread if you run across something that worked before but no longer does. If we don't know about a problem we can't fix it. Thank you.