Hi everybody! I'm in Siwa, and things are going well. The oasis is so much bigger and more prosperous than Tabelbala it seems almost decadent by comparison; its lakes and its expanses of groves suggest some idea of what Tabelbala's environment might have been like at its peak. The language is in no immediate danger; while some words are disappearing due to the great change in lifestyle, not only do children all seem to speak Siwi as a first language, but a substantial portion of the Shihaybat Bedouin settled in the western edge of Siwa learn it as a second one. However, the declining popularity of music at weddings may to some degree be threatening the vigorous local tradition of Siwi-language poetry. As Vycichl noted, Siwi has grammatically conditioned stress; in fact, you could argue that case is marked in Siwi by stress shifts. Siwi is definitely not mutually comprehensible with Kabyle, by the way - I've now tested this in both directions - nor with any Moroccan variety, according to local watchers of Moroccan satellite channels. Gara is also an interesting place - a much poorer, smaller oasis a hundred-odd km off, inhabited by mainly black people speaking Siwi. I've been there, but unfortunately security regulations more or less preclude spending the night.
The Bedouin Arabic of western Egypt is also of some interest. It is remarkably conservative, though not as much so as the dialects of Najd - it has a fully productive dual, distinguishes masculine and feminine plurals (both for verbal and adjectival agreement), and still has most short vowels. Technically, it shares some of the defining innovations of Maghrebi Arabic, in particular the 1st person plural n-...-uu; but it sounds scarcely closer to Algerian than even Cairene Arabic. They write a lot of poetry, some of it rather good. Inconveniently but interestingly, it appears that most Arabic influence on Siwi derives neither from their dialect nor from Cairene.
On a final note, anyone interested in medieval Berber history (there must be someone...) will recall the rather large Huwwara tribe (from which Houari Boumedienne ultimately got his nom de guerre). It turns out they're still very much around in the western Delta and even Upper Egypt, although they all speak Arabic now, as they had already begun to do in Ibn Khaldun's time; I met a Huwwari just the other day.