I've just tried this fix:  

1.) From the control panel select system and maintenance / device manager.

2.) Find the Dell Bluetooth module, right click on it and select properties.

3.) Go to the power management tab and de-select the checkbox against 'allow the computer to turn off this device to save power'. 

..........but unfortunately it hasn't worked. 

I have:

XPS M15302.5GHz Core 2 Duo

4Gb Ram

Windows Vista Home Premium

Dell Truemobile 355 Bluetooth + EDR

Microsoft Bluetooth Enumerator (whatever that is!!?)

....if you need to know my inside leg measurement to formulate a fix then please let me know!! 

The mouse and the XPS connected easy enough and didn't seem to give any problems.

However, it began freezing and does it randomly all the time. It even freezes mid-scroll through a document and has only narrowly escaped the fifteen floor drop to the street (on countless occasions) by the skin of it's flimsy Microsoft teeth!

Other devices in the Bluetooth inventory are my cell phone, who's sync software does not load to the system tray at start-up, and a Rikaline GPS receiver, both of which have been turned off the whole time.

I think it must be the mouse or mouse/laptop link as the track pad continues to work fine.

The daft thing is that, after following the above advice, I can leave the mouse immobile for more than 10 minutes and it moves straight away when I get back - but freezes when I'm actually mid-use!! Grrrrrrrrrrr!!!!!!!!! 

Microsoft are (not surprisingly in my experience) virtually impossible to get a straight answer from, so does anyone out there in Dell land have a fix?