I have seen people mention EXIF data and database features comparing Lightroom to CS5. Noone has mentioned the fact that CS5 comes with both ACR and Bridge. While I am sure Lightroom is a great program, these threads almost always gravitate towards the "Lightroom does everything Photoshop will do, aside from some stuff you don't need" which is a load of crap. CS5 is lightyears away from Lightroom. Its the same as when people say "Gimp is as good as CS5" All it boils down to, is whether you are a novice who wants very mild control of your photos, or whether you are aiming to be professional at some point and wanting extreme precision when altering your photos. Thats the simple choice between the two. Yes Photoshop has a bit more of a learning curve, but it also is like a scalpel compared to a butcher knife.
So if you have Elements 5 and think that will be sufficient then by all means use that. The best part is, you are getting that for free, so it doesn't hurt if you decide a month from now to move up to a higher level.