Individual framework components I've used in other projects include forms, database tools, i18n and l10n, authentication / authorization / session management and filters. These are all things that PW handles itself, so I don't really see much need for them anymore.
Things that I do still find useful, coming from Zend Framework, are it's web and web services components, such as Zend_Feed, Zend_Gdata (Google API tools) and HTTP, REST and XML-RPC clients. Also I could see some use for it's server tools, though I do admit that I've never had to use them before
@apeisa, that's a very good point, though I'd leave the "when you are not that seasoned developer" part away to keep things simple -- security experts (and common sense) have taught us that we shouldn't reinvent the wheel, even if it's fun. If we do, we're most likely going to make same mistakes that others have made (and fixed) before us. Not to mention that especially on client projects where time and money are limited a framework can lower production costs considerably and still keep quality high.
Naturally all of this mostly applies to serious stuff, client projects etc. Personal projects are very different matter