My experience indicates POJOs scale very well. And I mean, why wouldn't they? So long as you're not oblivious to
thread safety concerns, it should be fine.
Now, I've also used Spring with DWR, and I'm frankly not sure I like it more or less just yet. In some ways it's certainly nice (things like getting DataSource's in an object automatically is nice), but other things aren't (POJOs and DWR annotations means no config files, no extra "stuff" to think about). So I'm not passing judgement either way on that.
It all comes down I think to how you architect your application at a high level. If your client is doing most of the work, using the server, via DWR, as a service layer, which means you're using session sparringly, and you don't especially care about distributed execution where EJBs might actually make some sense (against what I believe to be typically true), then DWR with POJOs seems to be just the ticket.
If you have more specific concerns though I'd definitely be interested to hear them... I may be able to quell your fears a little, as it were, but you also might point out something I haven't thought of, which I'd appreciate for sure!
-- <br />Frank W. Zammetti<br />Founder and Chief Software Architect<br />Omnytex Technologies<br /><a href="http://www.omnytex.com" target="_blank" rel="nofollow">http://www.omnytex.com</a><br />AIM/Yahoo: fzammetti<br />MSN: fzammetti@hotmail.com<br />Author of "Practical Ajax Projects With Java Technology"<br /> (2006, Apress, ISBN 1-59059-695-1)<br />and "JavaScript, DOM Scripting and Ajax Projects"<br /> (2007, Apress, ISBN 1-59059-816-4)<br />Java Web Parts - <a href="http://javawebparts.sourceforge.net" target="_blank" rel="nofollow">http://javawebparts.sourceforge.net</a><br /> Supplying the wheel, so you don't have to reinvent it!