Within limits, Continental and Midwest allow 1:1 transfer of miles to Amtrak Guest Rewards. In that way (but not directly), you can use miles from those two airlines for US train travel still today.

As a further aisde, you can use BAA WorldPoints for discounts/upgrades on Heathrow Express, but BAA WorldPoints is an airport points program, not an airline miles program, and Heathrow Express is an airport-to-city train only.

But this example and Eurostar points out something: In Europe, most train systems from different countries overlap and are not the sort of thing for which you'd expect miles redemption. It's not surprising that the only example anyone has come up with so far is a premium stand-alone train like Eurostar. If there are other examples, I'd expect them probably only in the same catogory, such as Thalys. (AA used to have Thalys as a codeshare earning partner, but no longer for several years. AA still has SNCF and DB as codeshare earning partners, but none of these are or have been redemption partners.)

Prices on individual non-premium train trips in Europe are such that I would expect that if you could use miles for them, it'd be a pretty awful value (just as using miles for "permanently low fare" air markets like LAX-LAS would be a pretty awful value). And for lots of train trips during one visit, for people visiting from outside, rail passes often tend to be the way to get the best value. So that brings up the question: Any way to use any kind of miles or points for RailEurope or EuroRailways or any equivalent (not that I'd expect a great redemption value there either)?