Windows ReadyBoost + SD card faster than HDD = ?

Readyboost is only useful if you are running out of ram. If you still have plenty of ram left, using readyboost will have little or no effect. If you want to, give it a go.

The only way to speed up the hard drive is to replace it with a faster one. Readyboost will not speed up the hard drive at all. As shadow said, it's just a way to add temporary RAM.

I thought about that. That's my favorite argument against a full blown SSD. If I'm patient enough to wait out the first run, with enough RAM it should still be 'right there' in RAM.
I don't know enough about how RAM is used by the OS to be 100%; but it at least appears I 'run out' of RAM rather frequently.

Poorly optimized programs, such as Silverlight (or many PC games), often take up more and more RAM until I eventually (3+ hours in) I start dropping frames due to memory swaps (just like the old days)
Nothing short of some programming overhaul will fix things like that (properly clearing the RAM after each video);
certainly not an SD card.

Where I hope to gain some improvement is when sh***y programs like that push frequently used programs out; that the SD cache will store a copy paged faster than the HDD.
In a good cache system, one-time use data such as streaming video never gets written to it.

Also, unlike RAM, ReadyBoost cache won't be deleted on reboot.

(Also, my OEM claims my motherboard won't support more than 8 GB of RAM.)
(I am skeptical, since I doubt notebooks over 8 GB RAM use a different mobile chipset)

The normal ReadyBoost rules could be invalid.
In most cases, the HDD has faster sequential read/write speed, while the SD card has a shorter seek time and sometimes faster random read/write speed.

However, in this case, the SD card could be faster in ALL of these metrics.
As a cache, write speed of the SD card won't improve the overall system write speed.
This will always be limited by the system drive.

But random and sequential read from the SD card should easily trump the HDD; and if the OS (such as during system startup) read files saved on both drives.. it could cut startup time in half.

I can't help but think maybe Readyboost has been overlooked or forgotten; but might still have some valuable potential.

changing your harddrive will not invalidate a windows OEM license, only changing the motherboard will. if it for some reason doesn't want to activate you may have to call Microsoft but that's it. harddrives die after all. if you have an OEM disk/key you can install it. if it was an OEM system the factory restore disks MAY work. not sure on a smaller drive. you can also backup/delete data off the OS partition till it takes up less space than the size of the SSD and clone the OS to the SSD or restore an image to it using easeus Todo backup or partition manager, both free.

also SATAII will still allow around 350MB/s. there are plenty of SSDs that are SATA II and a SATAIII drive wont be hurt too much. just save yourself some money and don't buy the fastest since you'll be limited, just something midrange you can use. it will still be way way faster than a notebook drive. I still think they aren't worth the money and hassle (for me) but if you want one the concerns stopping you aren't really big issues.

Just posting to hopefully help someone else who stumbles upon this forum.
I have not tested readyboost, but like was said above if programs don't get loaded out of RAM because you aren't running out, then you woudln't even use it. You might be able to force windows to use the SD card as your only swap space and see a bit of improvement.
But I have put a crucial m4 SSD in a macbook Core2Duo 2.4Ghz with 8Gb of RAM.
I recently purchased a macbook i7 2.6Ghz with 16Gb of RAM.
The boot time, program execute time and shutdown time on the core2duo (slower computer) with the SSD is under half the time of the newer faster laptop.
You can breath new life into any machine that is at least SATA II with an SSD. The only problem most people have is capacity and price. In April 2013 an 7200 RPM laptop HDD is $0.20 - $0.25 per Gb whereas a SSD is still greater than $1 per Gb. If you don't use your optical drive then you could buy an adapter mount and put the SSD in place of your optical drive, have it boot and load the OS/programs from the SSD and use your HDD for storing all your files so you still keep the capacity you have while saving $$ by buying a smaller SSD. I'd suggest a 64Gb SSD as a bare minimum to run Windows. If you run Photoshop, or Do a lot of gaming then you'd probably want something bigger so you can keep the programs you run on the SSD for the added speed.