I realized that I'm going on and on in comments for no real reason but perhaps this is better suited for an answer.
The only Honeycomb build I'm aware of for the Tab is this one on XDA (there are two versions, GSM and CDMA). It is, for all intents and purposes, a bleeding-edge attempt to get Honeycomb running on the Tab. The developer refers to it as an "Alpha" and essentially says to expect things to be buggy.
Since there is no public source code for the 3.x releases of Android yet, the build is based on an extracted image/filesystem from the Android SDK, meaning that it is not optimized for the Tab and probably lacks 3rd party drivers (excepting any official 2.2 drivers that happen to be compatible with 3.x).
The GSM thread lists the following as "not working" under the current build, meaning this is the minimum you should expect to lose:
*Gyro (no rotation, there is an app installed but rotates wrong way)
*Settings window not appearing when expanding from the Notifications menu
*3g data nor phone abilities
*SD card on boot
In general, builds like this show up on devices when a new major release appears in the SDK but they tend to be fairly unstable and also fairly slow. The videos I've seen of this ROM appear a bit more performant (in general) than other SDK ports I've encountered, but your experience may vary.
As for restoring, the "Factory Reset" option doesn't usually touch system files on most devices, from what I know. It's possible I'm mistaken on this and that the Tab does actually restore the firmware, but I'm not incredibly familiar with the Tab. You'll probably want to do a little digging to see what a "Factory Reset" actually means (might be in your manual, perhaps).
That being said, there are instructions for getting a Verizon Tab back to stock here, and there might be similar ones floating around for other carriers. If you can get a custom recovery on to your device then you can simply back up your system before trying Honeycomb and then restore from the backup. The easiest way to do it is probably just to install ROM Manager and flash ClockworkMod recovery from there. There appear to be manual instructions about but they vary by carrier.
Personally speaking: I would not use an SDK port for anything other than showing off to people (which can admittedly be a whole lot of fun). In a production environment I definitely wouldn't risk it, and I honestly never kept them installed for more than about 30 or 45 minutes at a time to play with before restoring to a stable ROM. They were fun sneak-peaks, but I've always found them highly unreliable (though "your mileage may vary" is probably a good catch phrase here).
Edit: A word of caution to Wifi Tab users, this post on one of the Honeycomb threads indicates that the current ROMs (as of 6/19/2011) WILL NOT WORK on a Wifi Tab. I personally can not verify the validity of this statement, but this would not surprise me as other devices (e.g. the Xoom) have similar incompatibility among ROMs.