Hopefully you are not installing new x86 boxes, 64-bit handles memory so much better. If you have legacy x86 boxes you can easily do a backup or detach from that old system and restore or attach on the new x64 instance. You can also reverse the process and copy data from x64 back to x86. The same logic applies to the other technologies listed above.
Per BOL (I used the SQL 2008 R2 version):
· The SQL Server on-disk storage format is the same in the 64-bit and 32-bit environments. Therefore, a database mirroring session can combine server instances that run in a 32-bit environment and server instances that run in a 64-bit environment.
· Because the SQL Server on-disk storage format is the same in the 64-bit and 32-bit environments, a replication topology can combine server instances that run in a 32-bit environment and server instances that run in a 64-bit environment.
· The SQL Server on-disk storage format is the same in the 64-bit and 32-bit environments. Therefore, a log shipping configuration can combine server instances that run in a 32-bit environment and server instances that run in a 64-bit environment.
If you're doing SAN level replication you'll need to talk to your SAN vendor about their support across platforms.
Read more: Cindy Gross - Troubleshooting, tips, and general advice about SQL Server