I am using TRIM now (I assume), as I'm running the Ubuntu 10.10 kernel, which supports it on ext4. Before this, I was running 10.04, which didn't support trim. I'm not sure if I should clone the drive and reformat to get more speed, and I'm also not sure if there are alignment issues (I followed Ted Ts'o's advice on setting that up)...
Sorry if you have already done all this, but do you know if you are using the G1 or G2 X25-M? G1 doesn't have trim. G2 supports TRIM as long as you are not using the old firmware. So might be worth checking your firmware etc.?
Btw here is hdparm reading for my Western Digital Caviar Black (regular hard disk) just to give you an idea:
318 MB in 3.01 seconds = 105.56 MB/sec
I did upgrade my firmware a month ago, but I'm not sure which version I have, I'll check. However, now that you mention it, I do remember the disk doing 200ish mb/sec, maybe this was a fluke. It's almost empty, I use 20 out of the 160 gb, so I don't think it's a matter of allocated space...
As for your X25-M, do you have TRIM enabled? Your read speeds are consistent with a used-state SSD without TRIM.