I agree that UMDGEN is excellent. I am using version 4.0 without problems.
I convert to CSO to conserve space and havent run into any problems yet.
I Rip the update folder, the padding files, and ALL foreign languages.
On some games, you can save 500MB of space by removing the update and padding files, then by converting to CSO, save another 200MB.
Take Prince of Persia for example, save 500MB by deleting the update and padding, then compress to save even more.
An even better example is Legend of Heroes II. You can save almost a Gig worth of Memory by using the above method.
I have yet to experience lag using Sandisk gaming memory card 2GB.
Hope this helps.