I have made some quick benchmarks of my SD card on my Raspberry PI.

ionice -c 1 nice --20 hdparm -tT /dev/mmcblk0

/dev/mmcblk0:
 Timing cached reads:   280 MB in  2.00 seconds = 139.69 MB/sec
 Timing buffered disk reads:  32 MB in  3.13 seconds =  10.23 MB/sec
cat /sys/block/sda/queue/scheduler 
noop [deadline] cfq
./seeker /dev/mmcblk0
Seeker v2.0, 2007-01-15, http://www.linuxinsight.com/how_fast_is_your_disk.html
Benchmarking /dev/mmcblk0 [15193MB], wait 30 seconds
295223396
..............................
Results: 409 seeks/second, 2.443 ms random access time
for i in {1..32} ; do dd if=/dev/zero of=space.$i.4GiB.out bs=1M count=4096 ; done
4096+0 records in
4096+0 records out
4294967296 bytes (4.3 GB) copied, 802.682 s, 5.4 MB/s
^C902+0 records in
902+0 records out
945815552 bytes (946 MB) copied, 169.609 s, 5.6 MB/s
ionice -c 1 nice --20 bonnie++ -u root
Using uid:0, gid:0.
Writing a byte at a time...done
Writing intelligently...done
Rewriting...done
Reading a byte at a time...done
Reading intelligently...done
start 'em...done...done...done...done...done...
Create files in sequential order...done.
Stat files in sequential order...done.
Delete files in sequential order...done.
Create files in random order...done.
Stat files in random order...done.
Delete files in random order...done.
Version  1.96       ------Sequential Output------ --Sequential Input- --Random-
Concurrency   1     -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks--
Machine        Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP  /sec %CP
raspberrypi      1G    47  98  5095   7  3618   7   349  99 12698  11 485.6  56
Latency               472ms   13531ms    8527ms   37039us   47144us   56047us
Version  1.96       ------Sequential Create------ --------Random Create--------
raspberrypi         -Create-- --Read--- -Delete-- -Create-- --Read--- -Delete--
              files  /sec %CP  /sec %CP  /sec %CP  /sec %CP  /sec %CP  /sec %CP
                 16  2752  63 +++++ +++  4110  60  2599  58 +++++ +++  4003  60
Latency             14651us    8503us    5143us    6866us     394us    3927us
1.96,1.96,raspberrypi,1,1363919597,1G,,47,98,5095,7,3618,7,349,99,12698,11,485.6,56,16,,,,,2752,63,+++++,+++,4110,60,2599,58,+++++,+++,4003,60,472ms,13531ms,8527ms,37039us,47144us,56047us,14651us,8503us,5143us,6866us,394us,3927us