In the past 100 days for UK travel only:
UK & Ireland
http://www.flyertalk.com/forum/showthread.php?t=570999
http://www.flyertalk.com/forum/showthread.php?t=552688
http://www.flyertalk.com/forum/showthread.php?t=576341
http://www.flyertalk.com/forum/showthread.php?t=557219
London:
http://www.flyertalk.com/forum/showthread.php?t=581190
http://www.flyertalk.com/forum/showthread.php?t=567551
http://www.flyertalk.com/forum/showthread.php?t=577058
http://www.flyertalk.com/forum/showthread.php?t=574848
http://www.flyertalk.com/forum/showthread.php?t=573229
http://www.flyertalk.com/forum/showthread.php?t=568645
BD
http://www.flyertalk.com/forum/showthread.php?t=581887
http://www.flyertalk.com/forum/showthread.php?t=543571
http://www.flyertalk.com/forum/showthread.php?t=572976
http://www.flyertalk.com/forum/showthread.php?t=564360
http://www.flyertalk.com/forum/showthread.php?t=558955
http://www.flyertalk.com/forum/showthread.php?t=560404
http://www.flyertalk.com/forum/showthread.php?t=553645
http://www.flyertalk.com/forum/showthread.php?t=551216
http://www.flyertalk.com/forum/showthread.php?t=548469
Life was too short to check travelbuzz and BA, which are the other two fora we expect to see random UK rail questions. Also, Eurostar train questions can turn up on some of the European boards too... I also had to ignore some of the BD threads which turned into train discussions or discussions of train noises
since they weren't always readily apparent. I also left out local train/tube questions in London, and the debates about what should happen to GEX.
If this isn't considered sufficient to show interest, then perhaps Wingnut's idea of merging UK & Ireland with London would create a more natural home for train questions. As it is, this list does demonstrate the issue for train questions in the UK - there is no obvious place for them to go, which means the questions being asked, and answered are scattered across a number of boards, making finding searching for answers a lot more difficult. If you want to see what I mean, try searching for 'GNER' or 'Eurostar' - or indeed Virgin... who as well as being an airline, are one of the major long distance operators in the UK.
And that's the situation in the UK, doesn't even touch on the mainland Europe train stuff...