So far the only major problems I've run into is on 64-bit Office 2010 machines where Office has been installed in 64 bit mode. If that is the case, you will have a lot of problems with any older 32-bit operating system API calls that are in your code modules, and you will have to put compiler directives in (google #IF VBA7 and "pointer safe" for detailed info) the module headers so your code will know what to do, so it can run on either 32 or 64 bit platforms, for example:
#if VBA7 Then 'office 2010 machines not running in 32 bit emulation mode on 64 bit machines
Declare PtrSafe Function MyFunction Lib "my32BitLib.dll" (_
ByVal Key As LongPtr, ByVal SubKey As String, NewKey As LongPtr) _
As Long
#else
Declare Function MyFunction Lib "my32BitLib.dll" (_
ByVal Key As Long, ByVal SubKey As String, NewKey As Long) _
As Long
#endif
You might find that some libraries simply will bug out no matter what you do, but in my case most of the ones I had to junk applied to 3rd party PDF generators that are no longer needed since 2010 now natively generates PDF's without a need for third party libs.
I've also found that if you don't convert your databases to Access 2003, Access 2000 databases seem to run into all kinds of corruption issues when run under Access 2010, so find a machine running Access 2003 and run the dbs thru the converter. Other than that, if your code is real vanilla and doesn't use a lot of API calls, I've been surprised with how little trouble I've had with the conversion.