Edwin Khodabakchian, CEO of Collaxa, enumerates the shortcomings of BPELJ, a joint-proposal from BEA and IBM for skintight integration of BPEL and Java. In summary, BPELJ introduces new elements (code, value, package, snippet, etc.) for embedding and using Java code snippets in BPEL4WS files to specify variables, join conditions, partner links, correlation sets, and other extension points. Since Collaxa is the leading vendor of BPEL servers and tools for J2EE, Edwin's observations are important IMHO.
BTW, I have to note that the BPELJ whitepaper (PDF) does mention briefly about supporting other languages although I am not sure how deeply and sincerely that support is. After all, that 'J' in the name means something. In comparison, Biztalk use of CLR (.NET VM) supports multiple languages. Still, Biztalk is a wonderful sword with the vendor lock-in curse. BPELJ looks similarly cursed with Java language lock-in.
Is being locked-in vendor or language-wise really bad considering J2EE is a binding marriage with Java and most of the corporate IT shops are Microsoft addicts? I guess the answer depends on whether one cares about being tied down or not. After 12 years of marriage, I try not to think about the question too much. 🙂