This message is for OSX Server users.
The problems with Mavericks are completely different from the problems with Mountain Lion. I can tell you with absolute certainty that the new SMB system in Mavericks is not reliable with connected Windows computers.
If you desire to upgrade to Mavericks, I would strongly recommend that you perform the following steps before an upgrade. These will give you an immediate fallback option.
1. Configure three partitions. One for the sysetm, another for a system backup and a third for your data.
2. Clone your system partition to a new partition before the upgrade. CCCloner is a good tool for cloning the system partition.
3. Upgarde to Mavericks
4. When you are dissatisfied, switch your boot partition to the partition that you cloned in step one and you will be back to where you started before the update to Mavericks.
Of note:
Open Directory
OD is fragile. Any change to the hostname of your computer will break OD beyond repair (no changeip won't fix the problem). If you delete or change keychains used by OD or the Server app, OD can break. The only fix is to destroy your OD Master, export users and groups in Workgroup manager and re-import them after a new OD is built. Users will need to reset their passwords once complete.
About the only problem that can be solved without destroying your OD Master is a problem with forward or reverse DNS, which have to resolve to your machine's hostname.
Mavericks
File access seems OK until Windows machines attempt to load an executable file from the server. Also, some Windows applications do not seem to respect ACL's on the Mac server. I haven't found any solution to these issues. If you have Windows copmuters that need to access files on the Apple Server, I strongly urge everyone to postphone upgrades to Maverics.
Mountain Lion
Windows machines will loose connections to Mountain Lion Server during large file transfers or under load. The Windows registry can be modified to solve this problem as follows.
[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\services\LanmanWorkstation\Paramete rs]
"SessTimeout"=dword:00008ca0
"ExtendedSessTimeout"=dword:00008ca0
"ServersWithExtendedSessTimeout"=dword:00008ca0
"OffLineFileTimeoutIntervalInSeconds"=dword:00008ca0
It is a shame that Apple won't address these problems. The could have a great product here.