Some of Freddie Mac have a variable rate, that is, they "float" based on some index, say Libor or two-year Treasury bonds. Not saying you should avoid them, but if the dividends were ever restored, these preferreds would play a low dividend based on current market conditions.
The prospectuses for the preferreds are available here, just hit the link for the one you want to look at.
The preferreds have a redemption value of either $25 or $50. I believe they are all non-cumulative, meaning that the dividends that would have been paid during the September 2008 to present period are gone forever. Our preferreds are non-cumulative, which makes them quasi-equity, while cumulative preferreds are more like quasi-debt. By being non-cumulative, quasi-equity, they could be considered "core capital." The preferreds were "Tier 1" capital, which made them a favorable investment for commercial banks and similar investors, prior to the events in Sept 2008.
This is a good summary of the "macro" situation facing Freddie Mac. Figure 3 shows the projected combined cumulative Treasury draws for both enterprises.
One interesting thing is that Freddie Mac has done better than Scenario 1, which was the "best case" scenario. Also, note that Freddie Mac seemed to be in a better situation than Fannie. The impression this gives is that Freddie is essentially a year or two ahead of Fannie Mae, in terms of recovery.