I've had girlfriends tickle me repeatedly into oblivion, but I don't think they were what we'd call tickling enthusiasts... that's just something couples do to each other.
And I've had female friends tickle the living crap outta me, but same kinda deal... this is what friends do.
The ones I wonder about are the women I've worked with, mostly in office settings, who've taken it upon themselves to tickle me repeatedly and relentlessly, occasionally until I was on the verge of hysterics, in the office, at my desk, etc. Just as playful and friendly as the other instances, sure, but sometimes these are women I don't know as well as my friends; sometimes they're women I never see outside of the office. And yet they're tickling me a couple times a week. Might this reflect a more profound, more abiding interest in such activity, or are they just being playful and mischievous with a friendly colleague? (Or is the spectacle of my getting tickled more irresistably entertaining than I realize?? That seems unlikely.)