I vehemently disagree with that. Basel has expensive rent, but Zurich is higher. Regardless, like others said in the thread, 3500 gross will cut it for reasonable definitions of "stable living". It may not cut it for partying or for eating out often, perhaps.
With shared housing in Basel you can find something below CHF 1000 per month, perhaps as low as CHF 500.
Internet will be between CHF 20 and 60 CHF per month, but if you are sharing you may even get it at less than 20.
The insurance for international students can be had from Swisscare, will be under CHF 100 per month.
The food can be expensive but in Basel you can buy it from Germany easily.
Serious question, claudiaclause: are you really having trouble with expenses on your salary in Basel? What are you missing out on due to lack of funds? Feel free to PM me if you want to.
Emphasis here on "shared housing", because your salary will provide you stable living in Zurich when you look for roommate(s).
My husband finished his PhD at ETH and paid anywhere from CHF 700. - 900. for sharing a 2br unit in Oerlikon (far from campus but easily accessible via train/tram).
Just be warned that looking for roommates alone is a long and tedious process and may involve another round of interviews for you!
At ETH salaries change from department to department and professor to professor. I heard some maths PhD students have 5000 salary. But if your prof does not have that much money there's not much you can do about it. But you can try negotiating.
Usually CS and engineering get 100% and other departments less.
In Zurich rents are more expensive than in Basel (which I stated). In Basel it took me a while but I did find a non-shared place a good chunk cheaper than 1000 per month, and shared there were several options that I considered pretty decent that were also well under 1000 per month.
Still, I don't know what people here consider "unstable living" but even in Zurich I think a PhD student will be "stable" with CHF 1000 to 1500 left after rent and insurance for other living expenses (food etc.).
As students they probably get cheap/free access to several University Sports and according to another post on the thread they get a Halbtax card for transports as well. It won't necessarily be luxurious but I think it will be a pretty good salary compared to what PhD students make in many other countries, even with the higher cost of rent etc. accounted for.
1 and 2. This is a perfectly reasonable salary for a student. All of the Biochemistry students are currently on the 60% contract (which I was told gives around 3300 CHF net per month). Yes, they usually have roommates (as several have discusses). Yes, they also have vacations and nights out and a "stable" lifestyle. As BaselIPT mentioned, PhD students get free access to the ETH gyms, as well as reduced meal costs on campus.
3. Of course there are increases in salary by year of PhD. I'll post the source again.
4. There seems to be confusion about what salary means. Salary is set for PhD students (and postdocs) by the ETH. It's in the source document. Percentage is generally set by institute (not department-institutes are the smaller groups within departments). As mimimimi wrote, some departments (like Engineering) have generally higher percentages (mostly because it's hard to get PhD students at the 60% scale). chandra is writing from the postdoc perspective, in which there is considerably more leeway by professor-there is no consensus set by institute for postdoc contracts. Of course post-docs should try to increase their percentages. However, salary is still set by the ETH (see document). The only way to increase salary is if you have previous years of postdoc experience, which can be counted (and this is generally something that can be negotiated).
As a student, you cannot negotiate your salary. You may be able to negotiate percentage, but that's very unlikely to help (because of institute rules and because having students in the same group at different percentages is a bad idea in general). You can negotiate for equipment (say, a computer) or research related travel (say, one conference per year).
5. ETH generally does not allow higher salaries for PhDs or postdocs based on external funding. The exception is money that is not considered salary (for family, equipment, travel, etc.). This is because the salary is set.