LOB data on a different filegroup - performance issues/gains?

It really depends on the system. If you store a lot of LOB data and you can seperate this to a different drive and/or controller, you'll see a performance benefit. Also, it means you can backup that filegroup seperately from the others in the event you're looking at extremely large sets of data. The only con is the added overhead of maintaining additional drives and the extra work required when restoring the database because of the extra drives. In short, it can basically be all positive. In general, I consider it a best practice to seperate that type of storage into another file group.