Is he distracted, changed coach?
The Decline and Fall of Veselin Topalov

I think he has some motivation problems, he was world champion, won almost everything there is to win, became a multi millionaire, then lost the title. He got married and took a long vacation. Now what?
Anyway he's still 2750+, he's not fallen into any particularly deep abyss just yet.
Maybe he just isn't interested in working as hard as he once did now that he's married. He has looked a different player lately than the Topalov of 2005-08 that played some incredible games, for example this one:
http://www.chessgames.com/perl/chessgame?gid=1387655
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Already in 1994 Topalov won first board gold in the Chess Olympiad after beating Kasparov. He had an amazing year in 1996, winning five strong tournaments: shared first with Kasparov in Amsterdam with +4 in 9 games (Anand +1, Kramnik =, Gelfand -2); shared first with Kramnik in Dos Hermanas, ahead of Kasparov and Anand; sole first in Novgorod where Kramnik and Gelfand shared last; and shared first in Vienna and Leon. He reached 2750 on the July rating list and was only 35 points from Kasparov in first place.
Topalov had some good results the coming years but after 2004 he reached another level, and won lots of top tournaments. In 2005 he scored +4 together with Kasparov (after beating him) in Linares, and reached +6 as clear first in the FIDE World Championship in San Luis. He won Wijk (shared) both 2006 and 2007, Sofia three years in a row, and in 2008 he won both Grand Slam final and Nanjing while performing around 2900. Only Kasparov, Karpov and Fischer have been first on the rating list for a longer period than Topalov.
Topalov’s level started dropping visibly in 2010. He did win Linares even it was a comparatively weak edition, but in Nanjing he was only saved from finishing clear last by a blunder by Wang Yue in the final round, and in the Olympiad he was beaten by Bluvshtein. The title match was close, but maybe that had more to do with Anand losing a couple of games after uncharacteristic blunders than with Topalov being at his best.
In 2011 Topalov’s only individual classical event was Kazan, where he was beaten by Kamsky over four games. In Wijk this year he hasn’t yet won a game after ten rounds but lost two, and his live rating is down to 2757, approximately what it was 16 years ago. At the moment he is no longer top ten on the rating list, and the question is if he will ever return to something reminding of the level he once was. The way he has played most of the time after 2009 it is hard to see that happen.