Last week i was with a customer who had trouble developing his package because visual studio was very slow responding. This happens because SSIS Designer tries to connect to each data source that is used by your package to validate the metadata associated with sources and destinations. This causes validation errors when the data sources are not available or slow to respond when there are a lot of query’s (multiple dataflows) or big query’s.
I made a blog post a while ago that will make sure that the validation is postponed or not done at all:
Open SSIS packages without validation using the properties. This will speed things up a lot.