I am 3-4 years experienced Application developer in .NET. My friends are going to attend SAP classes and they are offering me to join them. Just was wondering if it is worth it putting it under my belt. They are attending FICO module. And I have taken 1-2 courses in Financial accounting during my school. What do you suggest?
I suggest you think about what do you want. Do you want to learn about SAP and its world of stuff including a lot of financial accounting stuff? Would you rather study something else? I'd probably consider what is the downside of taking the classes as I see at least a couple of upsides:
Expand your experiences beyond the .Net world. This can be quite advantageous in some cases if you want to be a consultant that has experience in various different platforms. This is appealing to the curiosity you may have about SAP.
Get into the SAP world. There are many customers of SAP software and having some experience in it may make you worth more to some employers, which may appeal to you being greedy in a sense.
In general SAP courses are very expensive (~$1000 a day), so considering the cost of the training offered by your friends as well.
If for some reason you can go on the course relatively cheaply it may be worthwhile if you would like to put it on your Resume. However I generally don't recommend doing a SAP course at your own expense before you at least have a system you can play on afterwards.
If you are truly interested in SAP there is a lot of information on SAP SDN. You can even download a Trial version with the ABAP development environment and have a bit of a play yourself.
Having some knowledge of SAP may be useful even as a .NET developer, the trick is to find what knowledge is going to be relevant to YOU.
The standard SAP FI/CO course has very little to do with programming and more to do with the data model and different configuration options. In general that module is aimed at people who would like to be SAP Functional Consultants in the FI Module. (I'm making some assumptions here, the course you're attending may not be the "standard" one at all).