I would not recommend mouseovers for healing outside of just starting out or raid healing.

For party based heals where time is critical across all 5 you should use something like this:

http://www.dual-boxing.com/threads/5...er-and-isboxer

That way your heals are immediate on the target and no fussing around with the mouse cursor during a heated battle. I found this necessary in PvP.

Basically my Naga 7-12 heal party with the remaining '8' key being my roaming mouseover / target / help or harm macro.

Then I mod Naga 7-12 to do other things like trinket, dispel, focus windows, etc. I drive 100% from healer so this was a good change for me. Though if you drive from the tank and use a healer like MW it should work just fine for you too.