Well, not quite—but I've reserved one.
We'll be going to Switzerland in August, and I'd looked around for various ticket options, and had all but decided to get a Swiss Half Fare Card for myself (essentially, a Halbtax for one month), since that would let me buy a day ticket for all of Switzerland on specific days. (The Swiss Card, which would offer the same, plus free travel from the airport to my destination and back on the first and last day, wouldn't have been worth it since a half-price return ticket costs less than the price difference between the SHFC and the SC.)
I could have got the Swiss Flexi Pass, which is essentially a Half Fare Card + a day ticket on three, four, five, or six specific days, but I had only planned two long trips (both to Grisons) and one shorter one (to Appenzell). Turned out that the SFP would probably have been a better value than SHFC + two all-network day tickets + one regional day ticket, but only barely.
But recently Peter called me up and said that he had spoken to Alvin and he had told him about special day tickets made available by many municipalities in Switzerland. He told me to google "Tages-GA" and "Gemeinde".
And bingo: talk about potluck! The ticket variously called a "Tages-GA" or "Tageskarte Gemeinde" works like this: municipalities that want to support public transport purchase a block of 365 pre-dated daily tickets from SBB, for round about 10'000 CHF. They then re-sell them to their inhabitants.
Different municipalities differ in the details; for example, some make the tickets available only to their own "citizens"; others make them available primarily to locals but will sell leftover tickets to non-locals when there are only two weeks (or whatever they decide) until the date on the ticket; some will offer two tickets a day while others will have ten or more; some will require you to show up and collect the ticket in person and pay in cash, while others accept credit card orders over the Internet and will sent the ticket by post; and even the price varies from place to place.
Turns out that Degersheim, where Peter lives, is pretty good for those tickets: they have comparatively many available (7 per day IIRC); they're fairly cheap (33 CHF when a typical price is 35 CHF, and a regular SBB day ticket [which requires you to have a Halbtax card] costs you 64 if you want to travel before 9 a.m.); you can reserve them over the Internet; and they don't require residence there as long as you can pick the tickets up in person. So I reserved some tickets in Peter's name and asked him to pick them up sometimes in the next four weeks or so, at his convenience, and I'll pay him back.
The most obvious disadvantage is that they're pre-dated and not refundable, so if you're ill that day or the weather is awful and you'd rather not go, you're stuck with them—and you can't count on purchasing them just a day or so in advance because the number of tickets per travel day is limited. But at that price difference (33 vs. 64, not even counting the 99 CHF you save by not having to buy the Swiss Half Fare Card), I think they're still a good idea.
So, now I know that I'll be travelling around Grisons on Wednesday, the 6th of August, with Peter and Debby; and that I'll be going there again myself on the following Wednesday, the 13th.
I just haven't decided where exactly. Top candidates are Juf (the highest continually-inhabited settlement in Switzerland, and possibly in Europe); Müstair and its monastery; Sta. Maria in Val Müstair; Malles/Mals over the border in South Tirol; and Scuol-Tarasp, possibly with Samnaun (where they speak Bairisch rather than Allemannisch).
Does anyone have any travel recommendations for Grisons? :D