The speed patch is a tiny bit of code that messes with the Linux task scheduler. There are many, many opinions about how scheduling should be managed, and no clear winners amongst them; the "speedpatch" merely replaces the default mechanism with one that the author of the code believed was better. Whether it is, in fact, better for you depends on how you use your device; however, given the way that it heavily skews scheduling towards just the user-facing tasks, I suspect that overall performance would actually drop. I want my N900 to perform all tasks in a timely manner, not just the one in current control of the GUI.

(One reason that you can't really multitask on other cell phones is to avoid even thinking about this problem; if you can't run tasks in the background, then you don't have to worry so much about scheduling tasks in the background. It's kind of amazing that people are still today crowing about the ability to run two apps at the same time on Android. I had to cringe when I watched a video demonstrating the upcoming BB10 OS, and one of the highly touted features was that "we will let you run EIGHT apps at the same time!" As if that were something to be amazed at.)

Honestly, if you want to actually run apps faster on the N900, there are only two useful methods. One, you can overclock the processor, to force commands to execute at a higher speed. Two, you can get involved with the remarkable effort undertaken to rebuild the Maemo system using the thumb2 instruction set. The N900's CPU had support for this more efficient command set from the start, but due to a few bugs, it was never used; due to the work of Freemangordon, however, an entire Maemo environment built using this instruction set is now becoming available.

In short, the "speed patch" and "battery patch" stuff is just snake oil. If you want to squeeze every last bit of performance out of your N900, you need to go with the guys who have put the real effort into creating an optimized system...