Where possible I take the train if it's a personal rather than a work trip, both for environmental reasons and because I find it less stressful (plus the fact that you see more). Obviously that isn't always an option, especially on a work trip if it's time-critical. I've just got back from a work trip to the Czech Republic, and am going to Switzerland for work early next month, so I am having to fly on both those occasions but at least this was my first flight for ten years and I haven't flown on a personal trip since 2005. At least for personal trips I can usually book them well in advance and get reasonably priced tickets.
Being based in Sheffield, and with my parents living in London, I can easily travel down to London and stay the night with them and then catch the Eurostar the next morning. Some of the trips that I've done in recent years going all the way by rail have included:
2006: London to Papiermühle, between Jena and Gera in eastern Germany, by Eurostar to Paris, the now withdrawn night train to Frankfurt, ICE to Weimar, then local train.
2009: London to Ede, Netherlands, using Eurostar to Brussels then Benelux IC.
2010: London to Stuttgart using Eurostar to Lille, TGV to Strasbourg, then local trains. One night in Stuttgart, then Stuttgart to Konstanz, returning from Konstanz via Karlsruhe, ICE to Brussels, then Eurostar.
2012: London to Niort, between Poitiers and La Rochelle, using Eurostar to Paris then TGV.
2013: London to Ede using the Harwich-Hook of Holland ferry.
2014: London to Auxerre, Burgundy, by Eurostar to Paris, then TER regional trains.
2016: London to Ede by Eurostar to Brussels and Benelux IC, then Arnhem to Zurich by the then soon to be withdrawn CityNightLine sleeper, Zurich to Konstanz, Konstanz to Radolfzell, Radolfzell to London via Basel, TGV to Paris and Eurostar.
2017: London to Prague using Eurostar to Paris, TGV to Karlsruhe, ICE to Zurich (terminated at Basel due to late running, so took regional train to Zurich), Zurich to Prague sleeper, then Prague to Dresden, Dresden to Jena, Jena to Ede (NL) and Ede-Brussels-London by Benelux IC and Eurostar.
At the end of this month I'm going to Luxembourg for the Trier area steam specials ("Dampfspektakel"), going by Eurostar to Brussels then Belgian IC train.
As someone mentioned earlier on this thread, the
www.seat61.com site is a useful source of reference. It tells you how to get to anywhere in Europe (and even some places outside Europe) without flying. In many cases you will find that it's easier and costs less than you think, especially if you factor in the time and cost of getting to and from airports (or parking at the airport if you drive there).