When you hit Cmd + E - or right-click the photo and select Edit in CS5 you should get a dialog box that gives you two options:
1) <Open anyway>, and
2) <Render using Lightroom>.
If you select (1) CS5 will open the original without Lr adjustments,
if you select (2) Lr will send a PSD to CS5 with all your Lr adjustments.
If you don't get this dialog because you have suppressed it, go >Edit >Preferences >General tab, and under the section "prompts" click on <Reset all warning dialogs>.