I have been using Sandisk products for a while and generally they great. However I made the mistake of purchasing the SanDisk Cruzer Slice 64 GB USB Flash Drive.
To put it simply, is very slow. Write speed, tested on several machines, is about 3.5-3.8MB/s. Read speed is much better at around 16MB/s.
The usable capacity is 59.6GB formatted. 59600MB @ 3.8Mb/s = 4.2 Hours (adjusted) to write 64GB of data.
Very high capacity, but not that usable day to day.