>>>>Yes, if your SQL Server is one of the listed. But this is still not recommended.
>>>
>>>Ok where are you seeing that its not recommended ?
>>>
>>>I haven't been able to find a reference to best practise about this.
>>
>>I believe I read this in many threads in Transact SQL forum at MSDN and could have read in other links as well.
>
>So its hearsay ?

We never disconnect users before rebuilding indexes. We run SQL Server Standard edition. Doing a rebuild causes the equivalent of a file lock (if I remember right), however, so long as the rebuild occurs quickly this hasn't been an issue for us. We only rebuild when fragmentation > 20%, otherwise we do a reorganize which doesn't require a file lock.