That seems pretty normal to me. A lot depends on the number of background processes you have running in addition to the programs you have opened. The number and types of desktop gadgets is also a factor. Right now I am running just my browser and using 3.252 Gigs of RAM.
Firefox (2 Tab), MS Word (2 documents, about 3 pages each), 3 PDF (in Adobe Acrobat X about 20 pages each) use up 2.62 GB of 8GB.
Only Firefox open (one tab, this page) it is 2.41GB of 8GB.