I've seen figures from that, to 5 or 10% of rating, to 5V or so...
There's not an electrode potential associated with it; or, if there is it's probably related to the electrolyte, maybe as an ionic bilayer or something, which will be good for a volt or two depending on electrolyte. So, it's not like it's exactly the 1.229V of water. (I don't actually know how much if any water they use in electrolytics, anyway? Mmh, probably mostly, still; just with enough stuff dissolved in it to raise the boiling point, at least for applicable (high temp) types.)
Also, [re]forming is a process that still works on finished capacitors; you can reverse one, and as long as it's done slowly enough (to avoid overheating, and allow gas to diffuse out), it will survive. If maybe not still within ratings (the cathode isn't textured so won't have as much capacitance as the anode does; the material is thinned in the process, perhaps increasing ESR, and certainly decreasing life; etc.).
Which is basically how bipolar electrolytics are made, as far as I know -- symmetrical (textured and formed) foils.
Electrolytics are certainly less sensitive than say tantalums, which can tolerate only a small reversal and don't [re]form (at least not in the same way) (so, are more likely to fail shorted [or worse]).
Tim