Snow Leopard users are a stubborn bunch.
I like to think I'm more "cautious" than "stubborn". I do plan on upgrading my SL 10.6.8 mid-2009 Macbook to Mavericks 10.9.3, mostly because fewer and fewer third-party programs I use are providing updates for SL (like VMware Fusion). But first I'm booting the MB off an external 10.9.2 drive to find out what kind of problems I can expect. And they can be considerable.
1) The new proprietary SMB2 file sharing (instead of Samba) means that I have to switch my Android devices to SFTP rather than CIFS to access files on the MB. I've tried several fixes relating to the /etc/nsmb.conf file, but none of them work form Android, while Samba worked great. Depending on how well SFTP works in the long run, I may have to use SMBUp to port Samba to Mavericks.
2) The native SSHD remote login no longer uses the simple "libwrap" mechanism to limit access, instead relying on the BSD "pf" packet filtering firewall. My BSD experience is limited, and I have yet to find a simple recipe to limit SSH access with pf. I may have to fall back to porting OpenSSH.
Other changes are more annoyances than dealbreakers, and can usually be disabled one way or another. Some of them are indicative of deeper issues, though, like how changing the hostname via "Sharing" preferences no longer changes the hostname universally (like in a Terminal window), and that change requires me to run "scutil". That's just Apple being sloppy, if you ask me.
Back to the third-party issue, I see that as more Apple's doing that the developers. Newer XCode's lack the SL development framework, which works fine when copied from an older XCode. Developers don't know that trick, though, try to make SL applications, but they crash, and they simply say "no more SL". Fusion is a special case, I'll admit, and supporting Fusion 6 is my main reason for updating to Mavericks. But I'm not enjoying it.
Last, I bought both Lion and Mountain Lion and decided not to update each time. The fact that I can update direct to Mavericks for free makes me feel like I paid to be an Apple beta tester. Not happy.