Ah,come on,where's your sense of adventure?
(Lol,just kidding.)
No,I believe that Microsoft.Windows.Exefile.HideExtension should not wreck your files and stuff,and if it was found during a scan and you were uncomfortable fixing it,you could choose not too.
Not much info on this one yet on the forums,I think it is new,so I added this to my own registry so Spybot would detect it,so you could see it(and I could see it too.)I'd assume that's right,since Spybot detected it.This is what was found after my scan:
Microsoft.Windows.Exefile.HideExtension: [SBI $ADD9B73B] Settings (Registry value, nothing done)
HKEY_CLASSES_ROOT\exefile\NeverShowExt
--- Spybot - Search & Destroy version: 1.5.2 (build: 20080128) ---
2008-01-28 blindman.exe (1.0.0.7)
2008-01-28 SDDelFile.exe (1.0.2.4)
2008-01-28 SDMain.exe (1.0.0.5)
2007-10-07 SDShred.exe (1.0.1.2)
2008-01-28 SDUpdate.exe (1.0.8.8)
2008-01-28 SDWinSec.exe (1.0.0.11)
2008-01-28 SpybotSD.exe (1.5.2.20)
2008-01-28 TeaTimer.exe (1.5.2.16)
2008-02-04 unins000.exe (51.49.0.0)
2008-01-28 Update.exe (1.4.0.6)
2008-01-28 advcheck.dll (1.5.4.5)
2007-04-02 aports.dll (2.1.0.0)
2007-11-17 DelZip179.dll (1.79.7.4)
2008-01-28 SDFiles.dll (1.5.1.19)
2008-01-28 SDHelper.dll (1.5.0.11)
2008-01-28 Tools.dll (2.1.3.3)
2008-04-16 Includes\Adware.sbi (*)
2008-04-24 Includes\AdwareC.sbi (*)
2008-04-24 Includes\Beta.sbi (*)
2007-11-06 Includes\Beta.uti (*)
2008-04-24 Includes\Cookies.sbi (*)
2007-12-26 Includes\Dialer.sbi (*)
2008-04-24 Includes\DialerC.sbi (*)
2008-04-24 Includes\HeavyDuty.sbi (*)
2008-03-19 Includes\Hijackers.sbi (*)
2008-04-24 Includes\HijackersC.sbi (*)
2008-02-27 Includes\Keyloggers.sbi (*)
2008-04-24 Includes\KeyloggersC.sbi (*)
2008-04-22 Includes\Malware.sbi (*)
2008-04-24 Includes\MalwareC.sbi (*)
2008-03-26 Includes\PUPS.sbi (*)
2008-04-24 Includes\PUPSC.sbi (*)
2008-04-24 Includes\Revision.sbi (*)
2008-01-09 Includes\Security.sbi (*)
2008-04-24 Includes\SecurityC.sbi (*)
2008-04-16 Includes\Spybots.sbi (*)
2008-04-24 Includes\SpybotsC.sbi (*)
2008-04-16 Includes\Spyware.sbi (*)
2008-04-24 Includes\SpywareC.sbi (*)
2007-11-06 Includes\Tracks.uti (*)
2008-04-24 Includes\Trojans.sbi (*)
2008-04-24 Includes\TrojansC.sbi (*)
2008-03-04 Plugins\Chai.dll
2008-03-05 Plugins\Fennel.dll
2008-02-26 Plugins\Mate.dll
2007-12-24 Plugins\TCPIPAddress.dll
There is more info here on NeverShowExt:
http://www.pctools.com/guides/registry/detail/627/
(That's just for general info,no need to follow it.)
I believe if the NeverShowExt value is added to HKEY_CLASSES_ROOT\exefile,that it hides the file extension of executables,which you probably would not want.
By default,HKEY_CLASSES_ROOT\exefile\NeverShowExt is probably not present in your registry and probably will not be detected(as far as I know),unless perhaps something malicious set it there,or you'd set that yourself.
However,if you had set the NeverShowExt value at HKEY_CLASSES_ROOT\exefile yourself,and did not want Spybot to fix it,you could add that to be ignored.There's a tutorial here on how to exclude products from the search.
http://www.safer-networking.org/en/howto/exclude.html
(If you wanted to add a product to Ignore single entries,you'd select Exclude this detection from further searches.)