MacPro5,1 3.2 GHz. For what is worth, I'm no expert but I spent a few days trying to find solutions, read this and many other forums and have the trackpad working to a point where is not acting up as much as before. The keypad remains intermittent while connected, but I still can use it to type this although it lags. Both the keypad and the trackpad exhibit the disconnected/connected behavior occasionally, this is more obvious when not in use for a few minutes. These are the following issues I found:
-Software: WD Quick View for Mac-latest release as of today. Using My Book Live: Removing this app improved the trackpad behavior significantly. I have the software now in Windows under Parallels. When this software is opened up in Windows it drives the trackpad bunkers! This is another example on how software can impact bluetooth.
-The Wi-Fi, that is usually off for me, seems to affect my trackpad and keypad when is on. There is discussion about how this is not possible (waves) but maybe is Yosemite.
-The closer the trackpad/keyboard are to the computer, the better they seem to work, although RSSI 70 seems to change little +/- 7. But there must be other issues (Yosemite) since it is intermittent. Shorty after bootup, while Yosemite is doing it's last bit of crunching, the trackpad acts up if you try to use it, but as soon as the computer calms down the trackpad works just fine. This acting up behavior was the one I had before all the time.
-I tried all the following, although is not clear to me if any one or the combination helped me out:
pre-boot/boot resets
unpairing/re-pairng (while holding the keyboard/trackpad on/off button down during the procedure)
trashed bluetooth
Yosemite full reinstall
OnyX cleanup (seem to bring some improvement as well)
A note about handoff:
I had handoff operational since Yosemite original installation, worked like a charm with my iPad & iPhone.
Lost the handoff after doing all the above. After a lot of reading someone recommended turning airdrop on for everybody
on the iPad & iPhone and it worked. There was an iCloud issue that I resolved by sending a sound to the iPad & iPhone from my MacPro.
Handoff now works as is supposed to again. I did get some 'Cocoa errors' but tried again and again until they went away. Note you will get these errors if you try to open mail that is not available (account) in the computer/device you are working on.
Apple really needs to come up with a fix for this.
Hope this helps someone out there.
Good luck!