more reasonably defaults for typical laptops (2 GB RAM, 2 cores);
enforce -server JVM if possible (NB: default JRE on Windows lacks that);

--- a/src/Tools/jEdit/dist-template/etc/settings	Tue Nov 16 10:33:36 2010 +0100
+++ b/src/Tools/jEdit/dist-template/etc/settings	Tue Nov 16 15:23:26 2010 +0100
@@ -4,8 +4,8 @@
 JEDIT_SETTINGS="$ISABELLE_HOME_USER/jedit"
 
 JEDIT_OPTIONS="-reuseview -noserver -nobackground"
-JEDIT_JAVA_OPTIONS="-Xms128m -Xmx512m -Xss2m -Dactors.corePoolSize=4 -Dactors.enableForkJoin=false"
-#JEDIT_JAVA_OPTIONS="-server -Xms128m -Xmx1024m -Xss4m -Dactors.corePoolSize=8 -Dactors.enableForkJoin=false"
+JEDIT_JAVA_OPTIONS="-Xms128m -Xmx1024m -Xss4m -Dactors.corePoolSize=4 -Dactors.enableForkJoin=false"
+#JEDIT_JAVA_OPTIONS="-Xms128m -Xmx512m -Xss2m -Dactors.corePoolSize=4 -Dactors.enableForkJoin=false"
 JEDIT_SYSTEM_OPTIONS="-Dapple.laf.useScreenMenuBar=true -Dcom.apple.mrj.application.apple.menu.about.name=Isabelle/jEdit"
 
 JEDIT_STYLE_SHEETS="$ISABELLE_HOME/lib/html/isabelle.css:$JEDIT_HOME/etc/isabelle-jedit.css:$ISABELLE_HOME_USER/etc/isabelle.css:$ISABELLE_HOME_USER/etc/isabelle-jedit.css"

--- a/src/Tools/jEdit/dist-template/lib/Tools/jedit	Tue Nov 16 10:33:36 2010 +0100
+++ b/src/Tools/jEdit/dist-template/lib/Tools/jedit	Tue Nov 16 15:23:26 2010 +0100
@@ -79,6 +79,9 @@
 declare -a JAVA_ARGS; eval "JAVA_ARGS=($JEDIT_JAVA_OPTIONS $JEDIT_SYSTEM_OPTIONS)"
 [ -n "$SCALA_HOME" ] && JAVA_ARGS["${#JAVA_ARGS[@]}"]="-Dscala.home=$SCALA_HOME"
 
+"$ISABELLE_TOOL" java -server >/dev/null 2>/dev/null && \
+  JAVA_ARGS["${#JAVA_ARGS[@]}"]="-server"
+
 declare -a ARGS; eval "ARGS=($JEDIT_OPTIONS)"
 
 declare -a OPTIONS; eval "OPTIONS=($ISABELLE_JEDIT_OPTIONS)"