By limerick standards our output is exceptionally clean. I think the occasional dive into the depths of depravity is necessary and indeed unavoidable. Citations:

[1.] The lim'rick packs laughs anatomical
In space that is quite economical,
But the good ones I've seen
So seldom are clean,
And the clean ones so seldom are comical.

[2.] Legman, who compiled the largest and most scholarly anthology, held that the true limerick as a folk form is always obscene, and cites similar opinions by Arnold Bennett and George Bernard Shaw, describing the clean limerick as a periodic fad and object of magazine contests, rarely rising above mediocrity.

That said, I don't think an excess of filth, whether or not it's folklorically accurate, is particularly funny either. One, or, perhaps I should say 'the MC community' needs mostly clean stuff to throw the filth into sharper relief. So I think my conclusion is to bring on the odd willy joke, and not to start complaining until we've had several in succession.

[Pen] I was about to agree wholeheartedly (and indeed KS's first line was singularly juvenile), but I went to the game and in fact there aren't any crude limericks currently on the top page. So, although I agree with your sentiment, you may actually be overstating the issue. Actually, I think we went through a dip into the area where saucy starts bordering on filthy a couple of weeks ago and have climbed out again.

Maybe you're influenced by the output on MCiOS - but I wouldn't class any of the currently visible lot as more than saucy.

Also, I don't actually think tits do like melons.

I'm with penelope in this instance. That line was pathetic, and completely out of keeping with the tone of the website.
More generally [SM] I believe your example #1 shows the type of limerick many of us prefer. The form may have its root in ribaldry, but there's a clear market for amusing rhymes and syllabic dexterity rather than innuendo.