I think the release notes will be the best place to look for.

6.5 was a major release of netbacklp while 6.5.3 is a patch.

Symantec has resolved many issues in each of the patches after 6.5 (sheduling being the biggest)

I would recommend you to go thought the release notes which will give all the bug fixes/enhancements done in each of the release.

big difference in NBU 6.0 and NBU 6.5 is of STORAGE LIFE CYCLE POLICIES.with this feature in NBU6.5 u can priortize ur duplication n deduplication with standard like gold silver bronze levels

With the launch of NBU 6.5 symantec is also trying to avoid tape backups[as first copy, offsite vaulting its tape everywhere] and aggresively marketing disk based backup.

nbu 6.5.3 is nbu6.5 with maintainence pack

difference in NBU 6.0 and NBU 6.5 is of  Media sharing and LiveUpdates with this feature in NBU6.5

from top of my head.
VCB backup for VMs, Storage life cycle, new improved policy manager.

SAN client backup(through fiber transport server)... Media sharing. improved nbpem..

The lastest version has fixes to problems found in previous versions.... nuf said!

addendum to Judy's postulation:
The latest version has problems to fix not found in the previous versions :-)

symantec always recommends that the newest version of NetBackup be loaded onto your systems. That way your production system can be a test sight for symantec and it benefits you by making you familiar with their support department. That being said, I like to wait and see how the community of users fare with a new relese before even putting it in the lab. This philosophy has kept me employed over the years.

I agree with Stumpr.  I usually am 1 version behind.  Watching from the side lines to see what issues other people that have upgraded are seeing.  I then upgrade when the next version comes out or I have to becuase I need the fix. 

Either way you should never be too far behind or you lose support at some point and are forced to quickly upgrade.

I concur with J Hinchcliffe's concurrance ;)

This is why I still run 6.5.2A and am only now starting to think about 6.5.3.1  (though i ran it on my test system for a while (as well as 6.5.4) and it seems ok)

I think the first thing is to realize what business requires, and check the compatibility matrix to find what choices you have.

For example, last year the company decided to move to Exchange 2007 on Windows 2008, and that was the main reason to upgrade to NetBackup 6.5 (actually, at least 6.5.2)since this is not supported with NetBackup 6.0.

And since 6.5.2 has bug introduced with the new pem code, we had to upgrade to 6.5.2a

Sometimes you just don't have much choice.

Normally i would always go a release behind.

Unfortunately I have many Windows DFR replication servers.
6.5.3 has a bug that gives exit code 0 but backs nothing up.

So I may go for 6.5.4. One of us has to be the 1st!

Other 6.5.x features that we need / add value are:

• Exchange 2007 support - be careful if you have exchange 5.5 backups are retired, only restores kept (for now)
• VMware VCB
• EVault email archiving support
• Storage lifecycles (can you spot the spelling mistake on the configuration popups?)
• Enhanced Advanced disk backups space efficiency
• Granular Active Directory restores
• Improved NOM
• Greyed out icons for inactive policies (small but very useful)  

Look at the Doc updates to see which incremental version is best for you.

http://seer.entsupport.symantec.com/docs/326269.htm

The 6.5.4 doc lists 6.5.3 & 6.5.2 updates & can help decide what features you need.

Rich

Normally i would always go a release behind.

Unfortunately I have many Windows DFR replication servers.
6.5.3 has a bug that gives exit code 0 but backs nothing up.

So I may go for 6.5.4. One of us has to be the 1st!

Other 6.5.x features that we need / add value are:

• Exchange 2007 support - be careful if you have exchange 5.5 backups are retired, only restores kept (for now)
• VMware VCB
• EVault email archiving support
• Storage lifecycles (can you spot the spelling mistake on the configuration popups?)
• Enhanced Advanced disk backups space efficiency
• Granular Active Directory restores
• Improved NOM
• Greyed out icons for inactive policies (small but very useful)  

Look at the Doc updates to see which incremental version is best for you.

http://seer.entsupport.symantec.com/docs/326269.htm

The 6.5.4 doc lists 6.5.3 & 6.5.2 updates & can help decide what features you need.

Rich

i've been on 6.5.3 for the last few months and had some weird problems where some databases would not backup. upgraded the master/media server to 6.5.4 and a lot of these problems went away

new versions have new bugs but at least they're supported.

we're still on v6.0 and considering the move to v6.5