Java 7 prevents Solr from indexing and causes lots of problems. So wait until Java 7 update 2 before upgrading.
http://lucene.apache.org/#28+July+2011+-+WARNING%3A+Index+corruption+and+crashes+in+Apache+Lucene+Core+%2F+Apache+Solr+with+Java+7
http://mail.openjdk.java.net/pipermail/hotspot-compiler-dev/2011-July/005971.html
