To make my test paypal shopping cart required some additional techniques I found here:
https://www.paypal.com/us/cgi-bin/webscr?cmd=p/xcl/rec/sc-techniques
You must be logged in to paypal to view this page.
Basically... the additional code was to be able to charge additional amounts for shirts larger than XL... which I did without problems.
I didn't use ALL of the techniques listed on these pages... however, they are not too difficult.
I really don't want to get into the paypal shopping cart versus other shopping cart debate.
This is my first t-shirt website... but I have sucessfully sold many other items online using paypal without problems after $1000's upon $1000's worth of transactions.
On the other hand... I am pretty proficient at web design... and I do a lot with templates.
For instance... Yesturday... it took me about an hour to add the modified paypal shopping cart code to about 88 pages of my site (that version is not online).
Once I got the code right for one product... I just pasted the code onto the other pages, then changed the item description... piece of cake.
Also... since my products are on their own pages... and not included in a shopping cart program... my site is very search engine friendly.
Heck... I am already in the top 3 to 8 for many of my keywords/phrases! Not bad for a site that isn't selling anything yet... (and yes... people are finding me... I track all traffic and referring sites/search engine pages.)
If you are not that website savvy... a self-contained shopping cart program that let's you add products easily may be the way to go.
Since I have been doing this web stuff since 1998... my ways are really easy for me... but don't always translate to other people's websites.
As always... your mileage may vary!

Brett