As with the 'Star Trek' connection, it was David Tennant's Doctor who strengthened the Toobworld link between 'Doctor Who' and 'The Hitch-Hiker's Guide To The Galaxy' (the TV version of Douglas Adams' masterwork).
When he snapped out of his coma after regeneration, the Doctor noted that the bathrobe he was wearing was similar to that worn by a friend of his - Arthur Dent. And this would the Dent, Arthur Dent of the TV series adaptation (at least vocally the same as the one to be found in the radio universe), and not the Arthur played by Martin Freeman in that botched movie version.
Again, as with the 'Star Trek' connection, the link to 'HHG2TG' was forged before the Tenth Doctor stepped out of the TARDIS - the Fourth Doctor was seen reading a book by the author Oolon Coluphid!
The Doctor : [Reading "Origins of the Universe"] "He got it wrong on the first line! Why didn't he ask someone who saw it happen?"
Also, one of the planets mentioned in "The Pirate Planet" is also where a key ingredient for a Pan Galactic Gargle-Blaster can be found.....
The Doctor - no matter which regeneration - probably met Arthur Dent due to Arthur's association with Ford Prefect and Zaphod Beeblebrox. Especially due to Ford Prefect - the tele-version of that fellow certainly looks like he had a lot in common with the Time Lord... at least sartorially....