I used to be surprised, and now am simply amused, when I hear the important kedushah prayer sung by the prayer leader to the tune of an Israeli love song. The most common is the song Erev Shel Shoshanim. It is possible that this tune was coopted from an earlier song that had no secular implications, but until someone provides me with details of this I will remain skeptical. Instead, I hear the whole congregation singing along (to the tune, not the words) and enjoying the soulful melody, while I’m left slightly amused and wondering what exactly a bustan is and why a couple would go out to one.
The halakhic question is whether it is permissible to use a secular tune from a love song for a prayer. I remember once as a teenager when someone slightly younger than me was leading services on Chol Ha-Mo’ed and started singing Hallel to the tune of Jingle Bells. Let’s just say that people stormed out in protest and when the rabbi learned of the incident the synagogue had some new policies (I wasn’t there but I heard all about it).
According to R. Moshe Feinstein (Iggeros Moshe, Yoreh Deah 2:111), because the actual singing itself is not for the purposes of a different religion, it is not technically forbidden. However, it is very distasteful (davar mekhu’ar). He says the same about secular songs, which would presumably include an Israeli love song. R. Yehudah Henkin (Bnei Banim 3:35:10) has a sensible approach to this very subject:
It is forbidden to use Non-Jewish songs — even if they are not love songs or Hebrew folk songs — as tunes for prayer if the congregation recognizes the songs and will think about the secular words during prayer time.
Since in my circles I’m probably the only one who knows the words to Israeli love songs, I guess the current practice is permissible according to R. Henkin and I’m out of luck.