I use a mix of Vista and XP. It seems to me that network latency is a huge factor so maybe UVNC has some weak error correcting code and cannot handle "delays". Thankfully for me, it is not a huge deal as I usually get around the situation. My last issue was about a week ago and I got around the problem by using Mozilla's FTP Zilla, which is free and allows multiple transfer threads. In the end, the issue with VNC improved my productivity by causing me to search for another product (bittersweet).
