Tridion migration Questions from SDL Tridion 5.3sp1 to 2011sp1

We have to migrate Tridion 5.3sp1 to 2011sp1,

if somebody have some experience on this kind of migration,

we are using only following features.

• DWT ( i dont see much changes in it)
• Tom.net
• TOM (TDSEClass)

what all needs to change? What are pain areas?

Where can i get more information online?

Based on my experience so far:

• TOM code will still work. You should rewrite it to use CoreService instead, but it doesn't have to be a priority, you can do this after upgrade. You really should do it anyway because it creates a dependency on COM+ which Tridion is phasing out. As far as I know, COM+ will be optional on the next Tridion release and possibly not available at all on the release after that.
• TOM.NET on templates might just work, but I think there were some changes done to the Filter classes from 5.3 to 2009. You may have to do a few small changes before it compiles again, nothing too serious.
• DWT: nothing changed

The biggest issues I've found are around the Event System. If you do have an old COM+ event system, it is still supported, but the cost of not upgrading to the new TOM.NET based event system shows up very quickly. COM+ errors/out of memory issues surface even faster with Tridion 2011 than they did before, it's like the COM to .NET Marshalling became less and less forgiving over time.

As Vikas says, the best way is to get an upgrade scan from people that have done this before, they know what the problem areas are, and quite frequently find extensions that you aren't even aware they were put in place, like Deployer extensions and "obscure" event systems or custom pages (or, from the good old R5 days, GUI hacks).