The problem I ran into with PayPal is that they required me to link my bank account directly to their service once I had reached a threshold dollar amount of usage (somewhere around $5000), rather than allowing me to leave just my credit card attached. This made me particularly nervous, as I have heard quite often of strange fees being applied with no recourse. If they only have access to my credit card, I would have more protection.
From Michael Anissimov on the Singularity Institute blog:
Thanks to generous contributions by our donors, we are only $11,840 away from fulfilling our $100,000 goal for the 2010 Singularity Research Challenge. For every dollar you contribute to SIAI, another dollar is contributed by our matching donors, who have pledged to match all contributions made before February 28th up to $100,000. That means that this Sunday is your final chance to donate for maximum impact.
Funds from the challenge campaign will be used to support all SIAI activities: our core staff, the Singularity Summit, the Visiting Fellows program, and more. Donors can earmark their funds for specific grant proposals, many of which are targeted towards academic paper-writing, or just contribute to our general fund
[Continue reading at the Singularity Institute blog.]