I generally advise people to avoid full justification of text online because:

• Research indicates it slows reading speed when used in printed materials
• Guidelines on web accessibility suggest that the ‘rivers of whitespace’ it creates are a distraction for users with certain types of cognitive impairments
• Several people with dyslexia have told me it makes following a line of text across the screen much harder (and I guess this is one of the reasons for the accessibility guideline).

After thinking about this some more, I thought it would be useful to see if I could dig up any of the research.  I put it on my ‘to-do’ list, but a quick search on Lord Google revealed some promising leads fairly quickly. I’ve yet to read these, but here’s the list for those who are interested.  I’ll post some summaries or tidbits when I do.

References

Bever, T. G., Jandreau, S., Burwell, R. , Kaplan, R., & Zaenan, A. (1990). Spacing printed text to isolate major phrases improves readability. Visible Language, 25, 74–87.

Coleman, E. B., & Kim, I. (1961). Comparison of several styles of typography in English. Journal of Applied Psychology, 45, 262–267.

Hartley, J. (1980). Spatial cues in text. Visible Language, 14, 67–79.

Hartley, J., & Burnhill, P. (1971). Experiments with unjustified text. Visible Language, 5, 265–278.

Jandreau, S., & Bever, T. G. (1992). Phrase-spaced formats improve comprehension in average readers. Journal of Applied Psychology, 77, 143–146.

Klare, G. R., Nichols, W. H., & Shufford, E. H. (1957). The relationship of typographic arrangement to the learning of technical material. Journal of Applied Psychology, 41, 41–45.

Mason, J. M., & Kendall, J. R. (1979). Facilitating reading comprehension through text structure manipulation. The Alberta Journal of Educational Research, 25, 68–76.

North, A. J., & Jenkins, L. B. (1951). Reading speed and comprehension as a function of typography. Journal of Applied Psychology, 35, 225–228.

• Beef up the first 11 characters of the link text
• Use specific, meaninful, action-oriented terms
• Use plain language
• Clearly differentiate links

The advice is based on testing truncated links from a broad range of sites with 80 users.

See: First 2 words: a signal for the scanning eye