Group work can be assessed as a single entity, a combination of individual and group achievement, or as individual achievement within the group. The choice of granularity of assessment is important. Grading schema must be clear to students who are understandably sensitive to receiving a lower grade than they feel they earned on a group project. Team evaluation can always be done on two bases: how well the group worked together to produce the product, and the quality of the product or output.
Where the group is assessed as a team, members can become more bonded and, where bonding and interactivity occur, the social context improves the quality of the learning experience. However, you need to prepare for the issue of the procrastinator or non-contributor who may reduce the team's motivation. The group must have some mechanism for managing if this problem affects performance. In the most extreme circumstance, you may allow the group to elect to work without the person who is not contributing, and you will need to arrange alternate work or a withdrawal from the student who is unable to participate. To avoid such situations, keep the tone positive and ensure that everyone understands what is expected.
You may elect to give separate grades, weighted as appropriate, to individual work and to work within the team. In this way, the grade for team that produces a quality product despite a non-contributor will not be reduced. Only the non-contributor will experience receiving a lower grade.
You can set out expectations for group performance, but assess students separately.
The contributions may be in the form of links to web sites, but contributions of ideas, new content, challenges to assumptions and synthesis of concepts and ideas are always important.