I had a pixi & a palm pre plus and loved both, but having 2 radios in the pixi die in 9 months was really annoying.
Made the switch to android and it was easy & fun. Sense on the Evo is just like synergy, but better and easier to link contacts. Gmail links wonderfully with calenders (remember that android is built by google)...I don't use yahoo or exchange, so I can't speak to those. Mail comes in right away for me, three different accounts, and no big drain on battery. I used to get about 10 hours on the palm phones, get the same on my evo - and that's running widgets & live wallpaper and using the net constantly.
Multitasking is different, but in terms of ease of use, it's the same. Instead of flicking through open apps, theres a long press of the home button. Some people complain it's not true multitasking because the app doesn't stay open if you leave it, but that's silly, IMO, because it opens back up where you left off...and it opens apps instantly, not like on webos where there is all that loading time.
Getting to learn android is not nearly as hard as some die hard palm people would lead you to believe. Loved webos, but nothing I miss about it as this phone can do sooo much.