http://en.wikipedia.org/wiki/Angels - basic info
http://www.catholic.com/library/Imma..._and_Assum.asp - theological debate about reason and the notion of no sin -
The objection is also raised that if Mary were without sin, she would be equal to God. In the beginning, God created Adam, Eve, and the angels without sin, but none were equal to God. Most of the angels never sinned, and all souls in heaven are without sin. This does not detract from the glory of God, but manifests it by the work he has done in sanctifying his creation. Sinning does not make one human. On the contrary, it is when man is without sin that he is most fully what God intends him to be.
Quoted from above article
From Wikipedia article on heaven -
heaven is a return to the pre-fallen state of humanity, a second and new Garden of Eden, in which humanity is reunited with God in a perfect and natural state of eternal existence.
All of this is part of a much larger religious debate, Ive been interested in theology for many years and thought Id share my views in regards to the forum topic. Cant recall every single source on the issue because Ive been reading about it for many years, but Wikipedia is generally my starting point because its such an excellent resource for information