Silvery - 4:35 pm on Aug 4, 2010 (gmt 0)
Thus far, I haven't seen any really strong correlation between getting into Google Maps and rankings within the regular keyword SERPs.
I believe that at most there could be an indirect correlation, because I believe that one of Googles 200+ ranking factors is clickthrough-by-keyword from their own search results pages. Under that theory, if you appear in the local 7-pack along with appearing in the regular keyword results, you're more likely to achieve more clickthroughs from your keyword phrases. The added clicks you might get from the 7pack could help to contribute towards ranking better in the regular results.
However, if clickthrough from SERPs is indeed a ranking factor (and I've argued the possibility with a number of other notable SEOs in the industry), then it appears to be a fairly weak factor which only has a marginal influence upon ranking.
It's also possible that if clickthroughs from SERPs are counted towards rankings that the clickthroughs from the 7pack might not be. It's very hard to differentiate clickthroughs from two different parts of the same SERP when attempting to study this possible behavior. So, it remains somewhat theoretical, while I still believe I see some indications that clickthroughs are incorporated into Google's overall ranking factors.
Endsum: Registration in Google Places might help your regular rankings, but if it does it's a very weak influence. Even so, it probably should be done as a part of your overall project because of the chance that Google could expand those local listings to take up nearly the entire first page of results (see my other post in this Local Search forum about Google's recent experiment in redesigning local SERPs).