I guess the writers need to find a happy medium with Horatio's screentime. Although, he did get quite a bit in season four, and they might just be taking it slowly with him this season. I'm betting they're keeping him out of the limelight because he'll have plenty of time onscreen when Yelina appears again.
I really do hope they include her in an investigation (hopefully not being the victim) so that she can work with Horatio again.
I've always enjoyed it when these two worked together on a case. Prime examples of that would be 'Money for Nothing', 'Dead Zone', 'Lost Son' just to name a few. I love the amount of professionalism they both show toward each other at work, and then in a moment, there is that tender silence between them and they no longer need words to communicate. Now THAT is chemistry you can't just make up and BAM it's in the script.
I believe that Yelina's return will be a great healing point in Horatio's life after losing Marisol. (I'm going to go with the fact that he 'loved her') I think after Yelina returns, Horatio will finally be able to move on, and to love again. Then we might be seeing the old Horatio again like he was before all of this season four debacle happened.
I agree with
Kit about Eric not objecting to seeing Horatio interact with Yelina again. He probably knew that they had something before she left.
...Anyway, now that I'm done rambling...Congrats on the new thread!