Upgrading a Mac running OS X 10.6-10.8 to Mavericks is not something I’d recommend without a compelling reason or solid upgrade plan. Reasons would include a necessary application that requires a newer version of OS X, or upgrading all the Macs within a workgroup to keep them consistent for an imaging solution.
Apple makes the upgrade process seem like it’s no big deal. They display the free Mavericks download prominently in the App Store when searching for Apple updates, which the Notification Center will redirect to if you click any of Apple’s “New OS X updates found” alerts… but I assure you that upgrading from one version of OS X to another is rarely a simple procedure.
Although Mavericks may be as stable as it’s going to get, now that the OS X 10.9.4 update is out, if you want to upgrade your Mac I would recommend two “at a minimum” steps. The first is making sure that every single application that you use is patched to the latest version before upgrading, and while doing so also verify each application version is compatible with Mavericks. Upgrading OS X, and then dealing with applications not working because they are unpatched or incompatible, is a common mistake leading to hours/days worth of frustration. The second “at a minimum” step I would recommend is having a full backup of the Mac saved to an external drive prior to upgrading (either with Time Machine or more preferably Carbon Copy Cloner). Upgrading OS X is a one-way path if you don’t have a backup, and those that experience major problems often wish they could just go back to the way things were. Having a full backup makes that possible.
Although I don’t recommend upgrading Macs to Mavericks just to get all the new bells and whistles… if you acknowledge that the journey may not be as smooth as promised, plus you follow my advice above, you should be fine in the long run. The one caveat is if you are using Apple Mail as your email client, and have a large amount of stored email or have a fairly complex setup (like multiple email accounts or numerous custom rules). Under this scenario you will likely you will run into headaches with Mail after upgrading to Mavericks. There doesn’t seem to be a common cause for these issues, and they can typically (but not always) be resolved using traditional troubleshooting methods, but they appear to be fairly widespread… and can take hours to fix.