If, as you say, it does not go to Kerry's campaign directly (i.e., if it's for a local or state office, as many efforts are):

Individual contribution limits

The following limits apply to contributions from individuals to candidates for all Federal offices.

$2,000 per Election to a Federal candidate -- Each primary, runoff, and general election counts as a separate election.

$5,000 per calendar year to a PAC or State party committee -- A PAC is a "Political Action Committee." PACs and party committees give the money you give them to candidates they support.

$25,000 per calendar year to a national party committee -- applies separately to a party's national committee, and House and Senate campaign committee.

$10,000 per calendar year to state, district & local party committees

$5,000 per calendar year to state, district & local party committee

Married couples are considered to be separate individuals with separate contribution limits.

(snip)

What constitutes a "contribution?"

Besides checks and currency, the FEC considers "...anything of value given to influence a Federal election" to be a contribution. Note that this does not include volunteer work. As long as you are not compensated for it, you can perform an unlimited amount of volunteer work.

Donations of food, beverages, office supplies, printing or other services, furniture, etc. are considered "in-kind" contributions, so their value counts against contribution limits.

And the $10,000 limit was based on what the person who was working there told me--I asked because I've given $2000 to Kerry.  Obviously people should ask the places that they're helping about the limits (if applicable).