I've seen "mouse skipping" and "keyboard stuck/repeat" issues with Bluetooth before (with multiple adapters, I bought more than one trying to fix it) due not to hardware or reception, as it seemed at the time... But in the end, due to drivers.
Did you ever install any proprietary drivers (branded) from the manufacturer of one of the dongles?
Bluetooth drivers seem to be a sketchy proposition at best, but I had this experience. I got an Apple Wireless Keyboard for my HTPC (by the way, love it and agree, that's the best living room keyboard), and I needed to get bluetooth, so I bought some cheap adapter off of Newegg.
It came with a disc. I never use the discs. In fact, I pick on my parents and joke when they call and start off:
"So I bought this new <INSERT CONSUMER ELECTRONICS OR COMPUTER DEVICE TYPE HERE> and I plugged it into my computer, and I can't get it to work right, and I did what it said and I put the disc in first, and-"
And I interrupt them and say, "You put in the disc? Never put in the disc. Especially when they seem to really want you to."
Anyhow...
I put in the disc. I know, right? Anyhow, I installed the driver from the disc in my excitement over playing with my new (and way too expensive) keyboard, and it installed some kind of weird crap in my system tray with a different driver interface from the standard Windows bluetooth setup, and I had these crappy keyboard repeat problems, and mouse issues and all sorts of things.
I tried everything, including uninstalling said drivers via Add/Remove control panel, moving the bluetooth adapter all around the room via powered hubs and active cables run under the floor and KVMs and all sorts of crazy stuff. I bought multiple adapters, including some way too expensive, hoping they'd be better.
The thing was, I knew it could work. I had Bluetooth on my Macbook Pro, iPhone, iPad, and my Lenovo and HP at the office. Same keyboard, same batteries, worked fine there. I was convinced it was the Bluetooth adapters, or the drivers or something.
Then one day I decided to solve it once and for all. I downloaded the drivers for one of my many adapters from the "manufacturer's" website and saved it, and then brought up a blank hard drive, disconnected my system drive, and installed a fresh copy of Windows. Now, when I did this, I'd left the Bluetooth dongle plugged into my machine. When Windows restarted and launched into the desktop for the first time, I watched it install some drivers, and rebooted and whatever...
Including Bluetooth... I hadn't installed my downloaded ones yet.
And my keyboard worked fine. And it kept working fine.
So then I went to work on my real install. Turned out, those initial crappy proprietary drivers I installed way back when were still "stuck" in there. Since almost all of the "manufacturers" of those dongles don't really make them, but just attach chips they bought from Broadcom to a USB port, wrap it in some plastic and send it out the door, most (if not all) of those dongles I bought had the same or similar chips inside, and were using the same crapped-up, stuck-in-there drivers.
I had to hunt them down manually, from within Safe mode, with the dongle detached, but I found them, and killed them, and then was able to install sane drivers and use the normal Windows control panel for Bluetooth and everything has been fine since. The Keyboard never loses sync (unless the batteries go totally dead), and I never get keyboard repeats or mouse problems (my mouse is now a Logitech one with a proprietary dongle, but the old ones were Bluetooth until they met a child-induced end).
I find, if you need to install drivers at all (Windows Update doesn't find them for you), use the drivers directly from Broadcom (or whomever your chip manufacturer happens to be) and they'll work best in almost all cases, not the ones from ASUS or Belkin or whoever-the-heck put their logo on the plastic thingy.