Hi BestofHarish,
1. You can find documentation on database portability at http://technet.microsoft.com/en-us/library/bb123954.aspx. This topic includes conceptual material that explains the process. It also includes a link to the procedural topic that walks you through database portability.
2. If a log cannot be replayed for any reason, it is kept in the InspectionFailed folder. See http://blogs.technet.com/scottschnoll/archive/2006/10/06/Exchange-2007-_2D00_-Continuous-Replication-Architecture-and-Behavior.aspx for more information on this.
3. You use /m:RecoverServer to recover a standalone system and /RecoverCMS to recover a clustered mailbox server. You cannot mix and match them (e.g., you cannot use /RecoverCMS to recover a standalone server). These switches are for recovery only, and cannot be used for conversion. See http://technet.microsoft.com/en-us/library/aa998656.aspx for more information.
4. /RecoverCMS is used to recover an entire clustered mailbox server. In fact, both Setup recovery options are used to recover a whole server; if you need to recover just some of the databases, you would use database portability. If you need to recover the whole server, then you would use the appropriate server recovery option.