>I've been writing some complex sp's and have started to incorporate some UDF's with them. This is kind of a general question but is there any significant performance differences?

I'm unaware of any prformance differences between SPs and UDFs but UDFs have a lot of restriction on which T-SQL statements/function can be used inside it.

>I read somewhere that you shouldnt use a UDF for data access. Just trying to get some opiniolns.

The UDFs have big negative impact on query performance. It's recomended to avoid using UDFs that are called for each record in the query. On other hand UDF can be used as parametrized view to return a recordset that can be used later in other query.