This last result is very interesting in that it shows it is possible to cheat at Rapidplay tempo at high level, however he is doing it.

Previously I had thought of rapidplay success as evidence against suspicious players being cheats, now will have to reconsider that.

nobody needs to follow engine for the best choice to cheat. 
if you have access to engine you can try different moves/ ideas  ( esp. if you are rated 2000+) and just make sure that engine shows + eval. 99 out of 100 opponents will eventual make a small mistake, then another one. And your moves will never be pegged as " computer moves" You can also avoid obvious " fritzy " moves as Anand said for that German cheat. 
In fact, if someone just knows to avoid obvious( to Houdini ) bad moves, this is enough for 2300, you'd draw and win most games.

8th round game:
Some say it's very interesting. 

8th round result:
5 12 IM Marholev Dimitar 2333 4½   0 - 1   4 Ivanov Borislav 2342 11

The 7th round game:

6th round result:
3 5 GM Popchev Milko 2434 3½   1 - 0   3½ Ivanov Borislav 2342 11

5th round victory as pgn:

...And some strange things continue to happen:

Name      Ivanov Borislav
Starting rank      11
Rating      2342
Rating national      2193
Rating international      2342
Ratingperformance      2403
FIDE rtg +/-      8.7
Points      3.5
Rank      6
Federation      BUL
Club/City      Viktory, Blagoevgrad
Ident-Number      1352
Fide-ID      2903741
 
Rd.      Bo.      SNo            Name      Rtg      FED      Pts.      Res.
1      10      27            Valkov Vladimir      2043      BUL      1.0      w ½
2      9      29            Kirchev Krasimir      1958      BUL      1.5      s 1
3      3      3      IM      Enchev Ivajlo      2441      BUL      3.5      s ½
4      7      9      IM      Kukov Velislav      2392      BUL      3.5      w ½
5      4      4      IM      Bratanov Zsivko      2438      BUL      2.5      w 1
6      3      5      GM      Popchev Milko      2434      BUL      3.5      s     (- tomorrow)

Taken from:
http://chess-results.com/tnr91883.aspx?art=9&lan=1&fed=BUL&wi=821&snr=11

Yes, probably very easy to do. Well not if the boards/receivers used some proper encryption but I have a bad feeling they probably didn't think of the need for that. They should!