SQL Server 2008 - How to convert GMT(UTC) datetime to local datetime?

You could do something like this:

declare @InputUtcDateTime datetime2 = '2011-05-20 06:30:18'

declare @LocalDateTime datetime2 = dateadd(minute, datepart(TZoffset, sysdatetimeoffset()), @InputUtcDateTime)
print @LocalDateTime

or

declare @InputUtcDateTime datetime2 = '2011-05-20 06:30:18'

declare @LocalDateTime datetime2 = dateadd(minute, datediff(minute, sysutcdatetime(), sysdatetime()), @InputUtcDateTime)
print @LocalDateTime

Aside from the Daylight Savings issue, why not simplify with:

yourDateTime - getutcdate() + getdate()